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 $65.74   7.269%   $70.5186   $70.52   $70.50   $70.50  
  Purchase #2 $88.33   3.168%   $91.1283   $91.13   $91.15   $91.10  
  Purchase #3 $114.52   11.439%   $127.6199   $127.62   $127.60   $127.60  
  Purchase #4 $190.80   7.521%   $205.1501   $205.15   $205.15   $205.20  
  Purchase #5 $57.79   6.417%   $61.4984   $61.50   $61.50   $61.50  
  Purchase #6 $153.41   5.600%   $162.001   $162.00   $162.00   $162.00  
  Purchase #7 $8.54   10.502%   $9.4369   $9.44   $9.45   $9.40  
  7 purchase totals = $679.13       $727.3532   $727.36   $727.35   $727.30