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 $56.82   4.662%   $59.4689   $59.47   $59.45   $59.50  
  Purchase #2 $195.46   11.703%   $218.3347   $218.33   $218.35   $218.30  
  Purchase #3 $95.25   13.654%   $108.2554   $108.26   $108.25   $108.30  
  Purchase #4 $104.50   5.393%   $110.1357   $110.14   $110.15   $110.10  
  Purchase #5 $80.94   4.118%   $84.2731   $84.27   $84.25   $84.30  
  Purchase #6 $224.27   4.386%   $234.1065   $234.11   $234.10   $234.10  
  Purchase #7 $241.75   9.555%   $264.8492   $264.85   $264.85   $264.80  
  7 purchase totals = $998.99       $1,079.4235   $1,079.43   $1,079.40   $1,079.40