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 $184.97   6.365%   $196.7433   $196.74   $196.75   $196.70  
  Purchase #2 $98.75   9.152%   $107.7876   $107.79   $107.80   $107.80  
  Purchase #3 $59.75   10.874%   $66.2472   $66.25   $66.25   $66.20  
  Purchase #4 $132.38   13.338%   $150.0368   $150.04   $150.05   $150.00  
  Purchase #5 $159.93   6.576%   $170.447   $170.45   $170.45   $170.40  
  Purchase #6 $213.51   11.376%   $237.7989   $237.80   $237.80   $237.80  
  Purchase #7 $22.60   9.736%   $24.8003   $24.80   $24.80   $24.80  
  7 purchase totals = $871.89       $953.8611   $953.87   $953.90   $953.70