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 $207.41   8.793%   $225.6476   $225.65   $225.65   $225.60  
  Purchase #2 $146.39   7.704%   $157.6679   $157.67   $157.65   $157.70  
  Purchase #3 $189.89   8.427%   $205.892   $205.89   $205.90   $205.90  
  Purchase #4 $131.88   11.522%   $147.0752   $147.08   $147.10   $147.10  
  Purchase #5 $11.35   6.833%   $12.1255   $12.13   $12.15   $12.10  
  Purchase #6 $197.76   10.343%   $218.2143   $218.21   $218.20   $218.20  
  Purchase #7 $61.43   10.660%   $67.9784   $67.98   $68.00   $68.00  
  7 purchase totals = $946.11       $1,034.6009   $1,034.61   $1,034.65   $1,034.60