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 $64.40   8.227%   $69.6982   $69.70   $69.70   $69.70  
  Purchase #2 $100.75   7.567%   $108.3738   $108.37   $108.35   $108.40  
  Purchase #3 $146.90   8.376%   $159.2043   $159.20   $159.20   $159.20  
  Purchase #4 $103.80   11.215%   $115.4412   $115.44   $115.45   $115.40  
  Purchase #5 $240.77   11.640%   $268.7956   $268.80   $268.80   $268.80  
  Purchase #6 $121.43   3.311%   $125.4505   $125.45   $125.45   $125.50  
  Purchase #7 $161.27   3.565%   $167.0193   $167.02   $167.00   $167.00  
  7 purchase totals = $939.32       $1,013.9829   $1,013.98   $1,013.95   $1,014.00