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 $245.94   11.530%   $274.2969   $274.30   $274.30   $274.30  
  Purchase #2 $156.61   9.605%   $171.6524   $171.65   $171.65   $171.70  
  Purchase #3 $74.85   12.400%   $84.1314   $84.13   $84.15   $84.10  
  Purchase #4 $213.32   9.704%   $234.0206   $234.02   $234.00   $234.00  
  Purchase #5 $43.90   10.500%   $48.5095   $48.51   $48.50   $48.50  
  Purchase #6 $20.80   12.443%   $23.3881   $23.39   $23.40   $23.40  
  Purchase #7 $95.91   11.776%   $107.2044   $107.20   $107.20   $107.20  
  7 purchase totals = $851.33       $943.2033   $943.20   $943.20   $943.20