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 $84.89   11.463%   $94.6209   $94.62   $94.60   $94.60  
  Purchase #2 $82.31   13.155%   $93.1379   $93.14   $93.15   $93.10  
  Purchase #3 $169.26   4.582%   $177.0155   $177.02   $177.00   $177.00  
  Purchase #4 $112.62   5.288%   $118.5753   $118.58   $118.60   $118.60  
  Purchase #5 $223.70   8.163%   $241.9606   $241.96   $241.95   $242.00  
  Purchase #6 $111.79   12.869%   $126.1763   $126.18   $126.20   $126.20  
  Purchase #7 $47.58   6.161%   $50.5114   $50.51   $50.50   $50.50  
  7 purchase totals = $832.15       $901.9979   $902.01   $902.00   $902.00