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 $175.82   6.654%   $187.5191   $187.52   $187.50   $187.50  
  Purchase #2 $106.62   12.375%   $119.8142   $119.81   $119.80   $119.80  
  Purchase #3 $157.87   13.509%   $179.1967   $179.20   $179.20   $179.20  
  Purchase #4 $201.45   7.193%   $215.9403   $215.94   $215.95   $215.90  
  Purchase #5 $150.78   8.325%   $163.3324   $163.33   $163.35   $163.30  
  Purchase #6 $13.58   12.179%   $15.2339   $15.23   $15.25   $15.20  
  Purchase #7 $158.64   13.805%   $180.5403   $180.54   $180.55   $180.50  
  7 purchase totals = $964.76       $1,061.5769   $1,061.57   $1,061.60   $1,061.40