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 $227.98   7.736%   $245.6165   $245.62   $245.60   $245.60  
  Purchase #2 $32.69   4.864%   $34.28   $34.28   $34.30   $34.30  
  Purchase #3 $150.90   8.246%   $163.3432   $163.34   $163.35   $163.30  
  Purchase #4 $125.85   11.392%   $140.1868   $140.19   $140.20   $140.20  
  Purchase #5 $213.43   8.391%   $231.3389   $231.34   $231.35   $231.30  
  Purchase #6 $11.73   12.436%   $13.1887   $13.19   $13.20   $13.20  
  Purchase #7 $143.58   7.270%   $154.0183   $154.02   $154.00   $154.00  
  7 purchase totals = $906.16       $981.9724   $981.98   $982.00   $981.90