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 $7.51   8.546%   $8.1518   $8.15   $8.15   $8.20  
  Purchase #2 $118.26   6.199%   $125.5909   $125.59   $125.60   $125.60  
  Purchase #3 $10.67   12.351%   $11.9879   $11.99   $12.00   $12.00  
  Purchase #4 $190.25   4.537%   $198.8816   $198.88   $198.90   $198.90  
  Purchase #5 $105.62   7.769%   $113.8256   $113.83   $113.85   $113.80  
  Purchase #6 $202.34   5.559%   $213.5881   $213.59   $213.60   $213.60  
  Purchase #7 $243.29   10.586%   $269.0447   $269.04   $269.05   $269.00  
  7 purchase totals = $877.94       $941.0706   $941.07   $941.15   $941.10