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 $88.43   4.263%   $92.1998   $92.20   $92.20   $92.20  
  Purchase #2 $234.99   10.196%   $258.9496   $258.95   $258.95   $258.90  
  Purchase #3 $136.44   6.451%   $145.2417   $145.24   $145.25   $145.20  
  Purchase #4 $119.55   3.500%   $123.7343   $123.73   $123.75   $123.70  
  Purchase #5 $93.80   11.698%   $104.7727   $104.77   $104.75   $104.80  
  Purchase #6 $231.75   10.222%   $255.4395   $255.44   $255.45   $255.40  
  Purchase #7 $59.58   9.494%   $65.2365   $65.24   $65.25   $65.20  
  7 purchase totals = $964.54       $1,045.5741   $1,045.57   $1,045.60   $1,045.40