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 $67.69   4.825%   $70.956   $70.96   $70.95   $71.00  
  Purchase #2 $168.78   12.391%   $189.6935   $189.69   $189.70   $189.70  
  Purchase #3 $75.67   7.350%   $81.2317   $81.23   $81.25   $81.20  
  Purchase #4 $95.73   11.843%   $107.0673   $107.07   $107.05   $107.10  
  Purchase #5 $187.59   6.278%   $199.3669   $199.37   $199.35   $199.40  
  Purchase #6 $250.29   4.859%   $262.4516   $262.45   $262.45   $262.50  
  Purchase #7 $109.29   10.693%   $120.9764   $120.98   $121.00   $121.00  
  7 purchase totals = $955.04       $1,031.7434   $1,031.75   $1,031.75   $1,031.90