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 $150.96   11.792%   $168.7612   $168.76   $168.75   $168.80  
  Purchase #2 $241.73   7.159%   $259.0355   $259.04   $259.05   $259.00  
  Purchase #3 $59.87   3.712%   $62.0924   $62.09   $62.10   $62.10  
  Purchase #4 $175.71   10.410%   $194.0014   $194.00   $194.00   $194.00  
  Purchase #5 $105.93   13.544%   $120.2772   $120.28   $120.30   $120.30  
  Purchase #6 $139.67   4.257%   $145.6158   $145.62   $145.60   $145.60  
  Purchase #7 $214.42   5.356%   $225.9043   $225.90   $225.90   $225.90  
  7 purchase totals = $1,088.29       $1,175.6878   $1,175.69   $1,175.70   $1,175.70