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 $61.84   10.641%   $68.4204   $68.42   $68.40   $68.40  
  Purchase #2 $165.28   11.471%   $184.2393   $184.24   $184.25   $184.20  
  Purchase #3 $24.96   12.204%   $28.0061   $28.01   $28.00   $28.00  
  Purchase #4 $115.99   7.810%   $125.0488   $125.05   $125.05   $125.00  
  Purchase #5 $239.83   10.815%   $265.7676   $265.77   $265.75   $265.80  
  Purchase #6 $51.79   11.498%   $57.7448   $57.74   $57.75   $57.70  
  Purchase #7 $200.75   8.107%   $217.0248   $217.02   $217.00   $217.00  
  7 purchase totals = $860.44       $946.2518   $946.25   $946.20   $946.10