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 $64.59   3.112%   $66.6   $66.60   $66.60   $66.60  
  Purchase #2 $82.86   10.504%   $91.5636   $91.56   $91.55   $91.60  
  Purchase #3 $164.51   6.861%   $175.797   $175.80   $175.80   $175.80  
  Purchase #4 $145.55   3.105%   $150.0693   $150.07   $150.05   $150.10  
  Purchase #5 $153.45   7.359%   $164.7424   $164.74   $164.75   $164.70  
  Purchase #6 $221.36   11.697%   $247.2525   $247.25   $247.25   $247.30  
  Purchase #7 $45.75   13.552%   $51.95   $51.95   $51.95   $52.00  
  7 purchase totals = $878.07       $947.9748   $947.97   $947.95   $948.10