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 $82.89   11.794%   $92.666   $92.67   $92.65   $92.70  
  Purchase #2 $188.86   11.715%   $210.9849   $210.98   $211.00   $211.00  
  Purchase #3 $48.27   8.422%   $52.3353   $52.34   $52.35   $52.30  
  Purchase #4 $242.25   10.301%   $267.2042   $267.20   $267.20   $267.20  
  Purchase #5 $109.76   13.660%   $124.7532   $124.75   $124.75   $124.80  
  Purchase #6 $5.50   8.423%   $5.9633   $5.96   $5.95   $6.00  
  Purchase #7 $227.92   4.473%   $238.1149   $238.11   $238.10   $238.10  
  7 purchase totals = $905.45       $992.0218   $992.01   $992.00   $992.10