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 $88.33   7.769%   $95.1924   $95.19   $95.20   $95.20  
  Purchase #2 $74.33   3.510%   $76.939   $76.94   $76.95   $76.90  
  Purchase #3 $124.55   3.580%   $129.0089   $129.01   $129.00   $129.00  
  Purchase #4 $159.40   12.299%   $179.0046   $179.00   $179.00   $179.00  
  Purchase #5 $23.29   4.667%   $24.3769   $24.38   $24.40   $24.40  
  Purchase #6 $33.37   3.266%   $34.4599   $34.46   $34.45   $34.50  
  Purchase #7 $246.94   7.362%   $265.1197   $265.12   $265.10   $265.10  
  7 purchase totals = $750.21       $804.1014   $804.10   $804.10   $804.10