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 $59.78   11.158%   $66.4503   $66.45   $66.45   $66.50  
  Purchase #2 $208.43   8.335%   $225.8026   $225.80   $225.80   $225.80  
  Purchase #3 $174.81   12.356%   $196.4095   $196.41   $196.40   $196.40  
  Purchase #4 $42.51   5.178%   $44.7112   $44.71   $44.70   $44.70  
  Purchase #5 $92.83   5.267%   $97.7194   $97.72   $97.70   $97.70  
  Purchase #6 $24.85   4.484%   $25.9643   $25.96   $25.95   $26.00  
  Purchase #7 $94.90   9.751%   $104.1537   $104.15   $104.15   $104.20  
  7 purchase totals = $698.11       $761.2110   $761.20   $761.15   $761.30