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 $123.59   7.406%   $132.7431   $132.74   $132.75   $132.70  
  Purchase #2 $95.81   10.792%   $106.1498   $106.15   $106.15   $106.10  
  Purchase #3 $200.64   8.830%   $218.3565   $218.36   $218.35   $218.40  
  Purchase #4 $13.59   10.367%   $14.9989   $15.00   $15.00   $15.00  
  Purchase #5 $143.80   3.774%   $149.227   $149.23   $149.25   $149.20  
  Purchase #6 $90.35   10.740%   $100.0536   $100.05   $100.05   $100.10  
  Purchase #7 $82.84   7.257%   $88.8517   $88.85   $88.85   $88.90  
  7 purchase totals = $750.62       $810.3806   $810.38   $810.40   $810.40