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 $213.52   11.611%   $238.3118   $238.31   $238.30   $238.30  
  Purchase #2 $204.36   7.347%   $219.3743   $219.37   $219.35   $219.40  
  Purchase #3 $107.75   11.229%   $119.8492   $119.85   $119.85   $119.80  
  Purchase #4 $210.42   4.425%   $219.7311   $219.73   $219.75   $219.70  
  Purchase #5 $91.58   13.765%   $104.186   $104.19   $104.20   $104.20  
  Purchase #6 $111.90   5.351%   $117.8878   $117.89   $117.90   $117.90  
  Purchase #7 $209.92   10.480%   $231.9196   $231.92   $231.90   $231.90  
  7 purchase totals = $1,149.45       $1,251.2598   $1,251.26   $1,251.25   $1,251.20