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 $97.95   4.462%   $102.3205   $102.32   $102.30   $102.30  
  Purchase #2 $85.65   12.140%   $96.0479   $96.05   $96.05   $96.00  
  Purchase #3 $240.88   4.567%   $251.881   $251.88   $251.90   $251.90  
  Purchase #4 $151.65   6.245%   $161.1205   $161.12   $161.10   $161.10  
  Purchase #5 $168.62   11.769%   $188.4649   $188.46   $188.45   $188.50  
  Purchase #6 $26.54   12.434%   $29.84   $29.84   $29.85   $29.80  
  Purchase #7 $23.71   3.313%   $24.4955   $24.50   $24.50   $24.50  
  7 purchase totals = $795.00       $854.1703   $854.17   $854.15   $854.10