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 $217.31   8.233%   $235.2011   $235.20   $235.20   $235.20  
  Purchase #2 $76.88   8.182%   $83.1703   $83.17   $83.15   $83.20  
  Purchase #3 $229.67   11.662%   $256.4541   $256.45   $256.45   $256.50  
  Purchase #4 $35.55   4.756%   $37.2408   $37.24   $37.25   $37.20  
  Purchase #5 $93.51   10.387%   $103.2229   $103.22   $103.20   $103.20  
  Purchase #6 $220.96   6.766%   $235.9102   $235.91   $235.90   $235.90  
  Purchase #7 $226.39   4.135%   $235.7512   $235.75   $235.75   $235.80  
  7 purchase totals = $1,100.27       $1,186.9506   $1,186.94   $1,186.90   $1,187.00