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 $246.69   12.290%   $277.0082   $277.01   $277.00   $277.00  
  Purchase #2 $237.38   7.504%   $255.193   $255.19   $255.20   $255.20  
  Purchase #3 $188.67   12.841%   $212.8971   $212.90   $212.90   $212.90  
  Purchase #4 $213.40   3.395%   $220.6449   $220.64   $220.65   $220.60  
  Purchase #5 $91.65   11.222%   $101.935   $101.94   $101.95   $101.90  
  Purchase #6 $92.61   11.599%   $103.3518   $103.35   $103.35   $103.40  
  Purchase #7 $204.33   8.628%   $221.9596   $221.96   $221.95   $222.00  
  7 purchase totals = $1,274.73       $1,392.9896   $1,392.99   $1,393.00   $1,393.00