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 $43.92   8.205%   $47.5236   $47.52   $47.50   $47.50  
  Purchase #2 $181.27   12.390%   $203.7294   $203.73   $203.75   $203.70  
  Purchase #3 $214.64   8.518%   $232.923   $232.92   $232.90   $232.90  
  Purchase #4 $195.95   3.143%   $202.1087   $202.11   $202.10   $202.10  
  Purchase #5 $87.65   11.320%   $97.572   $97.57   $97.55   $97.60  
  Purchase #6 $114.52   5.538%   $120.8621   $120.86   $120.85   $120.90  
  Purchase #7 $67.25   6.363%   $71.5291   $71.53   $71.55   $71.50  
  7 purchase totals = $905.20       $976.2479   $976.24   $976.20   $976.20