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 $49.94   5.348%   $52.6108   $52.61   $52.60   $52.60  
  Purchase #2 $164.99   13.244%   $186.8413   $186.84   $186.85   $186.80  
  Purchase #3 $119.38   9.832%   $131.1174   $131.12   $131.10   $131.10  
  Purchase #4 $120.49   12.581%   $135.6488   $135.65   $135.65   $135.60  
  Purchase #5 $13.71   11.277%   $15.2561   $15.26   $15.25   $15.30  
  Purchase #6 $176.29   5.362%   $185.7427   $185.74   $185.75   $185.70  
  Purchase #7 $204.49   5.533%   $215.8044   $215.80   $215.80   $215.80  
  7 purchase totals = $849.29       $923.0215   $923.02   $923.00   $922.90