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 $62.98   11.536%   $70.2454   $70.25   $70.25   $70.20  
  Purchase #2 $33.76   9.147%   $36.848   $36.85   $36.85   $36.80  
  Purchase #3 $108.71   11.401%   $121.104   $121.10   $121.10   $121.10  
  Purchase #4 $212.97   10.132%   $234.5481   $234.55   $234.55   $234.50  
  Purchase #5 $250.71   9.440%   $274.377   $274.38   $274.40   $274.40  
  Purchase #6 $172.76   9.621%   $189.3812   $189.38   $189.40   $189.40  
  Purchase #7 $53.95   7.466%   $57.9779   $57.98   $58.00   $58.00  
  7 purchase totals = $895.84       $984.4816   $984.49   $984.55   $984.40