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 $124.71   7.524%   $134.0932   $134.09   $134.10   $134.10  
  Purchase #2 $246.79   3.591%   $255.6522   $255.65   $255.65   $255.70  
  Purchase #3 $160.32   12.181%   $179.8486   $179.85   $179.85   $179.80  
  Purchase #4 $30.31   8.635%   $32.9273   $32.93   $32.95   $32.90  
  Purchase #5 $230.87   8.727%   $251.018   $251.02   $251.00   $251.00  
  Purchase #6 $185.54   13.163%   $209.9626   $209.96   $209.95   $210.00  
  Purchase #7 $58.58   7.815%   $63.158   $63.16   $63.15   $63.20  
  7 purchase totals = $1,037.12       $1,126.6599   $1,126.66   $1,126.65   $1,126.70