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 $224.99   9.513%   $246.3933   $246.39   $246.40   $246.40  
  Purchase #2 $61.55   5.110%   $64.6952   $64.70   $64.70   $64.70  
  Purchase #3 $227.91   3.626%   $236.174   $236.17   $236.15   $236.20  
  Purchase #4 $47.81   4.809%   $50.1092   $50.11   $50.10   $50.10  
  Purchase #5 $6.80   5.129%   $7.1488   $7.15   $7.15   $7.10  
  Purchase #6 $183.38   8.250%   $198.5089   $198.51   $198.50   $198.50  
  Purchase #7 $112.55   9.321%   $123.0408   $123.04   $123.05   $123.00  
  7 purchase totals = $864.99       $926.0702   $926.07   $926.05   $926.00