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 $73.61   4.461%   $76.8937   $76.89   $76.90   $76.90  
  Purchase #2 $192.83   8.399%   $209.0258   $209.03   $209.05   $209.00  
  Purchase #3 $56.78   11.489%   $63.3035   $63.30   $63.30   $63.30  
  Purchase #4 $232.71   11.491%   $259.4507   $259.45   $259.45   $259.50  
  Purchase #5 $218.55   13.149%   $247.2871   $247.29   $247.30   $247.30  
  Purchase #6 $93.93   8.270%   $101.698   $101.70   $101.70   $101.70  
  Purchase #7 $53.87   12.261%   $60.475   $60.48   $60.50   $60.50  
  7 purchase totals = $922.28       $1,018.1338   $1,018.14   $1,018.20   $1,018.20