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 $222.49   12.526%   $250.3591   $250.36   $250.35   $250.40  
  Purchase #2 $219.51   11.439%   $244.6197   $244.62   $244.60   $244.60  
  Purchase #3 $238.43   3.165%   $245.9763   $245.98   $246.00   $246.00  
  Purchase #4 $88.96   3.361%   $91.9499   $91.95   $91.95   $91.90  
  Purchase #5 $124.95   11.465%   $139.2755   $139.28   $139.30   $139.30  
  Purchase #6 $30.46   12.419%   $34.2428   $34.24   $34.25   $34.20  
  Purchase #7 $36.52   4.612%   $38.2043   $38.20   $38.20   $38.20  
  7 purchase totals = $961.32       $1,044.6276   $1,044.63   $1,044.65   $1,044.60