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 $52.98   13.287%   $60.0195   $60.02   $60.00   $60.00  
  Purchase #2 $25.31   6.835%   $27.0399   $27.04   $27.05   $27.00  
  Purchase #3 $235.31   3.400%   $243.3105   $243.31   $243.30   $243.30  
  Purchase #4 $245.88   5.444%   $259.2657   $259.27   $259.25   $259.30  
  Purchase #5 $244.34   12.804%   $275.6253   $275.63   $275.65   $275.60  
  Purchase #6 $141.99   6.783%   $151.6212   $151.62   $151.60   $151.60  
  Purchase #7 $17.45   12.138%   $19.5681   $19.57   $19.55   $19.60  
  7 purchase totals = $963.26       $1,036.4502   $1,036.46   $1,036.40   $1,036.40