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 $141.39   7.275%   $151.6761   $151.68   $151.70   $151.70  
  Purchase #2 $164.29   13.213%   $185.9976   $186.00   $186.00   $186.00  
  Purchase #3 $54.63   13.619%   $62.0701   $62.07   $62.05   $62.10  
  Purchase #4 $57.43   8.105%   $62.0847   $62.08   $62.10   $62.10  
  Purchase #5 $247.25   12.108%   $277.187   $277.19   $277.20   $277.20  
  Purchase #6 $88.71   4.850%   $93.0124   $93.01   $93.00   $93.00  
  Purchase #7 $89.86   6.305%   $95.5257   $95.53   $95.55   $95.50  
  7 purchase totals = $843.56       $927.5536   $927.56   $927.60   $927.60