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 $125.38   5.829%   $132.6884   $132.69   $132.70   $132.70  
  Purchase #2 $243.80   13.423%   $276.5253   $276.53   $276.55   $276.50  
  Purchase #3 $179.43   11.809%   $200.6189   $200.62   $200.60   $200.60  
  Purchase #4 $84.68   12.241%   $95.0457   $95.05   $95.05   $95.00  
  Purchase #5 $242.42   12.594%   $272.9504   $272.95   $272.95   $273.00  
  Purchase #6 $223.50   12.340%   $251.0799   $251.08   $251.10   $251.10  
  Purchase #7 $68.32   6.874%   $73.0163   $73.02   $73.00   $73.00  
  7 purchase totals = $1,167.53       $1,301.9249   $1,301.94   $1,301.95   $1,301.90