Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $196.35   8.124%   $212.3015   $212.30   $212.30   $212.30  
  Purchase #2 $164.53   3.731%   $170.6686   $170.67   $170.65   $170.70  
  Purchase #3 $197.64   11.224%   $219.8231   $219.82   $219.80   $219.80  
  Purchase #4 $115.42   6.798%   $123.2663   $123.27   $123.25   $123.30  
  Purchase #5 $197.31   6.800%   $210.7271   $210.73   $210.75   $210.70  
  Purchase #6 $119.61   11.779%   $133.6989   $133.70   $133.70   $133.70  
  Purchase #7 $126.83   8.679%   $137.8376   $137.84   $137.85   $137.80  
  7 purchase totals = $1,117.69       $1,208.3231   $1,208.33   $1,208.30   $1,208.30