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 $233.79   12.713%   $263.5117   $263.51   $263.50   $263.50  
  Purchase #2 $177.95   8.851%   $193.7004   $193.70   $193.70   $193.70  
  Purchase #3 $87.27   4.492%   $91.1902   $91.19   $91.20   $91.20  
  Purchase #4 $25.96   5.804%   $27.4667   $27.47   $27.45   $27.50  
  Purchase #5 $142.54   12.486%   $160.3375   $160.34   $160.35   $160.30  
  Purchase #6 $62.66   11.185%   $69.6685   $69.67   $69.65   $69.70  
  Purchase #7 $18.70   10.580%   $20.6785   $20.68   $20.70   $20.70  
  7 purchase totals = $748.87       $826.5535   $826.56   $826.55   $826.60