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 $91.43   3.559%   $94.684   $94.68   $94.70   $94.70  
  Purchase #2 $98.87   13.336%   $112.0553   $112.06   $112.05   $112.10  
  Purchase #3 $62.56   13.601%   $71.0688   $71.07   $71.05   $71.10  
  Purchase #4 $151.47   6.194%   $160.8521   $160.85   $160.85   $160.90  
  Purchase #5 $30.92   7.135%   $33.1261   $33.13   $33.15   $33.10  
  Purchase #6 $249.83   3.278%   $258.0194   $258.02   $258.00   $258.00  
  Purchase #7 $235.34   12.244%   $264.155   $264.16   $264.15   $264.20  
  7 purchase totals = $920.42       $993.9607   $993.97   $993.95   $994.10