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 $68.38   3.615%   $70.8519   $70.85   $70.85   $70.90  
  Purchase #2 $203.26   12.675%   $229.0232   $229.02   $229.00   $229.00  
  Purchase #3 $165.76   12.789%   $186.959   $186.96   $186.95   $187.00  
  Purchase #4 $33.54   7.777%   $36.1484   $36.15   $36.15   $36.10  
  Purchase #5 $53.29   5.487%   $56.214   $56.21   $56.20   $56.20  
  Purchase #6 $156.49   11.533%   $174.538   $174.54   $174.55   $174.50  
  Purchase #7 $33.26   10.687%   $36.8145   $36.81   $36.80   $36.80  
  7 purchase totals = $713.98       $790.5490   $790.54   $790.50   $790.50