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 $64.65   13.716%   $73.5174   $73.52   $73.50   $73.50  
  Purchase #2 $153.32   4.325%   $159.9511   $159.95   $159.95   $160.00  
  Purchase #3 $174.91   4.237%   $182.3209   $182.32   $182.30   $182.30  
  Purchase #4 $195.38   5.395%   $205.9208   $205.92   $205.90   $205.90  
  Purchase #5 $172.44   5.586%   $182.0725   $182.07   $182.05   $182.10  
  Purchase #6 $8.31   6.835%   $8.878   $8.88   $8.90   $8.90  
  Purchase #7 $91.94   10.302%   $101.4117   $101.41   $101.40   $101.40  
  7 purchase totals = $860.95       $914.0724   $914.07   $914.00   $914.10