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 $209.38   8.554%   $227.2904   $227.29   $227.30   $227.30  
  Purchase #2 $21.65   13.388%   $24.5485   $24.55   $24.55   $24.50  
  Purchase #3 $103.99   11.818%   $116.2795   $116.28   $116.30   $116.30  
  Purchase #4 $41.60   10.173%   $45.832   $45.83   $45.85   $45.80  
  Purchase #5 $232.52   5.228%   $244.6761   $244.68   $244.70   $244.70  
  Purchase #6 $114.25   8.762%   $124.2606   $124.26   $124.25   $124.30  
  Purchase #7 $166.29   13.629%   $188.9537   $188.95   $188.95   $189.00  
  7 purchase totals = $889.68       $971.8408   $971.84   $971.90   $971.90