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 $204.37   13.767%   $232.5056   $232.51   $232.50   $232.50  
  Purchase #2 $30.84   10.510%   $34.0813   $34.08   $34.10   $34.10  
  Purchase #3 $57.90   8.374%   $62.7485   $62.75   $62.75   $62.70  
  Purchase #4 $103.29   3.106%   $106.4982   $106.50   $106.50   $106.50  
  Purchase #5 $247.81   11.433%   $276.1421   $276.14   $276.15   $276.10  
  Purchase #6 $93.81   12.534%   $105.5681   $105.57   $105.55   $105.60  
  Purchase #7 $136.44   10.355%   $150.5684   $150.57   $150.55   $150.60  
  7 purchase totals = $874.46       $968.1122   $968.12   $968.10   $968.10