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 $185.46   8.127%   $200.5323   $200.53   $200.55   $200.50  
  Purchase #2 $217.76   6.648%   $232.2367   $232.24   $232.25   $232.20  
  Purchase #3 $43.44   7.733%   $46.7992   $46.80   $46.80   $46.80  
  Purchase #4 $194.84   7.173%   $208.8159   $208.82   $208.80   $208.80  
  Purchase #5 $33.79   8.348%   $36.6108   $36.61   $36.60   $36.60  
  Purchase #6 $116.69   6.821%   $124.6494   $124.65   $124.65   $124.60  
  Purchase #7 $166.78   4.661%   $174.5536   $174.55   $174.55   $174.60  
  7 purchase totals = $958.76       $1,024.1979   $1,024.20   $1,024.20   $1,024.10