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 $95.50   8.196%   $103.3272   $103.33   $103.35   $103.30  
  Purchase #2 $181.70   9.550%   $199.0524   $199.05   $199.05   $199.10  
  Purchase #3 $244.52   6.148%   $259.5531   $259.55   $259.55   $259.60  
  Purchase #4 $48.43   9.328%   $52.9476   $52.95   $52.95   $52.90  
  Purchase #5 $146.55   7.263%   $157.1939   $157.19   $157.20   $157.20  
  Purchase #6 $100.81   12.226%   $113.135   $113.14   $113.15   $113.10  
  Purchase #7 $78.80   11.681%   $88.0046   $88.00   $88.00   $88.00  
  7 purchase totals = $896.31       $973.2138   $973.21   $973.25   $973.20