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 $94.49   10.417%   $104.333   $104.33   $104.35   $104.30  
  Purchase #2 $192.64   4.421%   $201.1566   $201.16   $201.15   $201.20  
  Purchase #3 $144.82   8.736%   $157.4715   $157.47   $157.45   $157.50  
  Purchase #4 $149.56   7.371%   $160.5841   $160.58   $160.60   $160.60  
  Purchase #5 $241.81   6.804%   $258.2628   $258.26   $258.25   $258.30  
  Purchase #6 $210.89   11.260%   $234.6362   $234.64   $234.65   $234.60  
  Purchase #7 $226.49   12.646%   $255.1319   $255.13   $255.15   $255.10  
  7 purchase totals = $1,260.70       $1,371.5761   $1,371.57   $1,371.60   $1,371.60