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 $85.72   9.321%   $93.71   $93.71   $93.70   $93.70  
  Purchase #2 $149.29   8.304%   $161.687   $161.69   $161.70   $161.70  
  Purchase #3 $138.75   12.266%   $155.7691   $155.77   $155.75   $155.80  
  Purchase #4 $244.32   11.660%   $272.8077   $272.81   $272.80   $272.80  
  Purchase #5 $198.97   3.336%   $205.6076   $205.61   $205.60   $205.60  
  Purchase #6 $107.54   5.270%   $113.2074   $113.21   $113.20   $113.20  
  Purchase #7 $6.59   13.573%   $7.4845   $7.48   $7.50   $7.50  
  7 purchase totals = $931.18       $1,010.2733   $1,010.28   $1,010.25   $1,010.30