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 $224.67   11.299%   $250.0555   $250.06   $250.05   $250.10  
  Purchase #2 $97.41   4.237%   $101.5373   $101.54   $101.55   $101.50  
  Purchase #3 $159.25   9.587%   $174.5173   $174.52   $174.50   $174.50  
  Purchase #4 $184.43   9.118%   $201.2463   $201.25   $201.25   $201.20  
  Purchase #5 $22.52   7.774%   $24.2707   $24.27   $24.25   $24.30  
  Purchase #6 $195.49   12.623%   $220.1667   $220.17   $220.15   $220.20  
  Purchase #7 $31.82   11.783%   $35.5694   $35.57   $35.55   $35.60  
  7 purchase totals = $915.59       $1,007.3632   $1,007.38   $1,007.30   $1,007.40