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 $68.59   5.390%   $72.287   $72.29   $72.30   $72.30  
  Purchase #2 $218.99   12.561%   $246.4973   $246.50   $246.50   $246.50  
  Purchase #3 $67.45   11.578%   $75.2594   $75.26   $75.25   $75.30  
  Purchase #4 $62.93   4.820%   $65.9632   $65.96   $65.95   $66.00  
  Purchase #5 $229.37   8.185%   $248.1439   $248.14   $248.15   $248.10  
  Purchase #6 $103.70   4.590%   $108.4598   $108.46   $108.45   $108.50  
  Purchase #7 $6.31   10.397%   $6.9661   $6.97   $6.95   $7.00  
  7 purchase totals = $757.34       $823.5767   $823.58   $823.55   $823.70