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 $59.74   5.861%   $63.2414   $63.24   $63.25   $63.20  
  Purchase #2 $146.37   4.377%   $152.7766   $152.78   $152.80   $152.80  
  Purchase #3 $9.86   9.733%   $10.8197   $10.82   $10.80   $10.80  
  Purchase #4 $250.61   9.565%   $274.5808   $274.58   $274.60   $274.60  
  Purchase #5 $158.84   12.849%   $179.2494   $179.25   $179.25   $179.20  
  Purchase #6 $155.73   9.517%   $170.5508   $170.55   $170.55   $170.60  
  Purchase #7 $143.83   3.814%   $149.3157   $149.32   $149.30   $149.30  
  7 purchase totals = $924.98       $1,000.5344   $1,000.54   $1,000.55   $1,000.50