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 $166.61   11.835%   $186.3283   $186.33   $186.35   $186.30  
  Purchase #2 $83.35   12.659%   $93.9013   $93.90   $93.90   $93.90  
  Purchase #3 $183.87   11.691%   $205.3662   $205.37   $205.35   $205.40  
  Purchase #4 $7.79   4.506%   $8.141   $8.14   $8.15   $8.10  
  Purchase #5 $204.51   7.494%   $219.836   $219.84   $219.85   $219.80  
  Purchase #6 $95.56   13.251%   $108.2227   $108.22   $108.20   $108.20  
  Purchase #7 $214.91   11.448%   $239.5129   $239.51   $239.50   $239.50  
  7 purchase totals = $956.60       $1,061.3084   $1,061.31   $1,061.30   $1,061.20