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 $59.27   7.164%   $63.5161   $63.52   $63.50   $63.50  
  Purchase #2 $210.98   10.503%   $233.1392   $233.14   $233.15   $233.10  
  Purchase #3 $112.61   12.316%   $126.479   $126.48   $126.50   $126.50  
  Purchase #4 $46.94   13.386%   $53.2234   $53.22   $53.20   $53.20  
  Purchase #5 $28.27   10.313%   $31.1855   $31.19   $31.20   $31.20  
  Purchase #6 $156.63   12.110%   $175.5979   $175.60   $175.60   $175.60  
  Purchase #7 $219.83   8.832%   $239.2454   $239.25   $239.25   $239.20  
  7 purchase totals = $834.53       $922.3865   $922.40   $922.40   $922.30