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 $63.36   7.482%   $68.1006   $68.10   $68.10   $68.10  
  Purchase #2 $58.37   12.472%   $65.6499   $65.65   $65.65   $65.60  
  Purchase #3 $43.56   7.850%   $46.9795   $46.98   $47.00   $47.00  
  Purchase #4 $184.49   6.402%   $196.301   $196.30   $196.30   $196.30  
  Purchase #5 $236.43   12.113%   $265.0688   $265.07   $265.05   $265.10  
  Purchase #6 $193.78   11.385%   $215.8419   $215.84   $215.85   $215.80  
  Purchase #7 $17.25   7.819%   $18.5988   $18.60   $18.60   $18.60  
  7 purchase totals = $797.24       $876.5405   $876.54   $876.55   $876.50