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 $73.83   4.126%   $76.8762   $76.88   $76.90   $76.90  
  Purchase #2 $222.41   5.806%   $235.3231   $235.32   $235.30   $235.30  
  Purchase #3 $44.29   9.760%   $48.6127   $48.61   $48.60   $48.60  
  Purchase #4 $103.67   10.134%   $114.1759   $114.18   $114.20   $114.20  
  Purchase #5 $166.93   3.802%   $173.2767   $173.28   $173.30   $173.30  
  Purchase #6 $8.37   5.453%   $8.8264   $8.83   $8.85   $8.80  
  Purchase #7 $204.60   4.678%   $214.1712   $214.17   $214.15   $214.20  
  7 purchase totals = $824.10       $871.2622   $871.27   $871.30   $871.30