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 $203.54   6.717%   $217.2118   $217.21   $217.20   $217.20  
  Purchase #2 $140.49   4.772%   $147.1942   $147.19   $147.20   $147.20  
  Purchase #3 $84.32   7.479%   $90.6263   $90.63   $90.65   $90.60  
  Purchase #4 $162.55   4.385%   $169.6778   $169.68   $169.70   $169.70  
  Purchase #5 $58.94   6.425%   $62.7269   $62.73   $62.75   $62.70  
  Purchase #6 $133.55   12.533%   $150.2878   $150.29   $150.30   $150.30  
  Purchase #7 $182.25   3.304%   $188.2715   $188.27   $188.25   $188.30  
  7 purchase totals = $965.64       $1,025.9963   $1,026.00   $1,026.05   $1,026.00