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 $64.36   8.132%   $69.5938   $69.59   $69.60   $69.60  
  Purchase #2 $114.96   4.423%   $120.0447   $120.04   $120.05   $120.00  
  Purchase #3 $201.48   6.551%   $214.679   $214.68   $214.70   $214.70  
  Purchase #4 $88.92   11.388%   $99.0462   $99.05   $99.05   $99.00  
  Purchase #5 $142.85   5.246%   $150.3439   $150.34   $150.35   $150.30  
  Purchase #6 $236.35   6.248%   $251.1171   $251.12   $251.10   $251.10  
  Purchase #7 $69.75   6.736%   $74.4484   $74.45   $74.45   $74.40  
  7 purchase totals = $918.67       $979.2731   $979.27   $979.30   $979.10