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 $54.46   11.437%   $60.6886   $60.69   $60.70   $60.70  
  Purchase #2 $95.80   9.361%   $104.7678   $104.77   $104.75   $104.80  
  Purchase #3 $88.95   7.213%   $95.366   $95.37   $95.35   $95.40  
  Purchase #4 $170.52   8.765%   $185.4661   $185.47   $185.45   $185.50  
  Purchase #5 $35.28   12.381%   $39.648   $39.65   $39.65   $39.60  
  Purchase #6 $192.95   12.757%   $217.5646   $217.56   $217.55   $217.60  
  Purchase #7 $194.72   7.335%   $209.0027   $209.00   $209.00   $209.00  
  7 purchase totals = $832.68       $912.5038   $912.51   $912.45   $912.60