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 $171.26   11.530%   $191.0063   $191.01   $191.00   $191.00  
  Purchase #2 $92.34   3.179%   $95.2755   $95.28   $95.30   $95.30  
  Purchase #3 $157.42   8.191%   $170.3143   $170.31   $170.30   $170.30  
  Purchase #4 $46.75   8.737%   $50.8345   $50.83   $50.85   $50.80  
  Purchase #5 $109.69   7.482%   $117.897   $117.90   $117.90   $117.90  
  Purchase #6 $244.97   12.432%   $275.4247   $275.42   $275.40   $275.40  
  Purchase #7 $238.88   12.580%   $268.9311   $268.93   $268.95   $268.90  
  7 purchase totals = $1,061.31       $1,169.6834   $1,169.68   $1,169.70   $1,169.60