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 $13.26   11.265%   $14.7537   $14.75   $14.75   $14.80  
  Purchase #2 $107.43   10.150%   $118.3341   $118.33   $118.35   $118.30  
  Purchase #3 $227.40   3.332%   $234.977   $234.98   $235.00   $235.00  
  Purchase #4 $211.71   7.832%   $228.2911   $228.29   $228.30   $228.30  
  Purchase #5 $142.52   8.291%   $154.3363   $154.34   $154.35   $154.30  
  Purchase #6 $14.75   3.802%   $15.3108   $15.31   $15.30   $15.30  
  Purchase #7 $66.44   4.301%   $69.2976   $69.30   $69.30   $69.30  
  7 purchase totals = $783.51       $835.3006   $835.30   $835.35   $835.30