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 $59.31   12.187%   $66.5381   $66.54   $66.55   $66.50  
  Purchase #2 $205.47   9.832%   $225.6718   $225.67   $225.65   $225.70  
  Purchase #3 $102.43   8.205%   $110.8344   $110.83   $110.85   $110.80  
  Purchase #4 $157.78   5.204%   $165.9909   $165.99   $166.00   $166.00  
  Purchase #5 $45.81   9.260%   $50.052   $50.05   $50.05   $50.10  
  Purchase #6 $113.93   13.796%   $129.6478   $129.65   $129.65   $129.60  
  Purchase #7 $5.44   12.540%   $6.1222   $6.12   $6.10   $6.10  
  7 purchase totals = $690.17       $754.8572   $754.85   $754.85   $754.80