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 $41.56   13.131%   $47.0172   $47.02   $47.00   $47.00  
  Purchase #2 $220.90   9.636%   $242.1859   $242.19   $242.20   $242.20  
  Purchase #3 $235.85   6.207%   $250.4892   $250.49   $250.50   $250.50  
  Purchase #4 $203.92   13.701%   $231.8591   $231.86   $231.85   $231.90  
  Purchase #5 $27.81   5.637%   $29.3776   $29.38   $29.40   $29.40  
  Purchase #6 $40.41   7.210%   $43.3236   $43.32   $43.30   $43.30  
  Purchase #7 $123.39   7.107%   $132.1593   $132.16   $132.15   $132.20  
  7 purchase totals = $893.84       $976.4119   $976.42   $976.40   $976.50