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 $61.57   11.169%   $68.4468   $68.45   $68.45   $68.40  
  Purchase #2 $146.98   9.857%   $161.4678   $161.47   $161.45   $161.50  
  Purchase #3 $181.82   5.360%   $191.5656   $191.57   $191.55   $191.60  
  Purchase #4 $44.44   3.566%   $46.0247   $46.02   $46.00   $46.00  
  Purchase #5 $13.39   7.692%   $14.42   $14.42   $14.40   $14.40  
  Purchase #6 $183.73   10.640%   $203.2789   $203.28   $203.30   $203.30  
  Purchase #7 $26.77   5.474%   $28.2354   $28.24   $28.25   $28.20  
  7 purchase totals = $658.70       $713.4392   $713.45   $713.40   $713.40