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 $224.37   3.713%   $232.7009   $232.70   $232.70   $232.70  
  Purchase #2 $58.32   4.867%   $61.1584   $61.16   $61.15   $61.20  
  Purchase #3 $175.62   12.686%   $197.8992   $197.90   $197.90   $197.90  
  Purchase #4 $236.37   7.508%   $254.1167   $254.12   $254.10   $254.10  
  Purchase #5 $164.88   6.143%   $175.0086   $175.01   $175.00   $175.00  
  Purchase #6 $29.96   9.579%   $32.8299   $32.83   $32.85   $32.80  
  Purchase #7 $119.44   6.806%   $127.5691   $127.57   $127.55   $127.60  
  7 purchase totals = $1,008.96       $1,081.2828   $1,081.29   $1,081.25   $1,081.30