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 $212.41   3.214%   $219.2369   $219.24   $219.25   $219.20  
  Purchase #2 $16.57   11.850%   $18.5335   $18.53   $18.55   $18.50  
  Purchase #3 $238.97   13.778%   $271.8953   $271.90   $271.90   $271.90  
  Purchase #4 $215.52   9.771%   $236.5785   $236.58   $236.60   $236.60  
  Purchase #5 $45.39   3.428%   $46.946   $46.95   $46.95   $46.90  
  Purchase #6 $31.53   3.334%   $32.5812   $32.58   $32.60   $32.60  
  Purchase #7 $219.61   3.850%   $228.065   $228.07   $228.05   $228.10  
  7 purchase totals = $980.00       $1,053.8364   $1,053.85   $1,053.90   $1,053.80