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 $94.50   10.282%   $104.2165   $104.22   $104.20   $104.20  
  Purchase #2 $166.56   4.793%   $174.5432   $174.54   $174.55   $174.50  
  Purchase #3 $223.74   9.174%   $244.2659   $244.27   $244.25   $244.30  
  Purchase #4 $61.95   11.615%   $69.1455   $69.15   $69.15   $69.10  
  Purchase #5 $161.61   8.847%   $175.9076   $175.91   $175.90   $175.90  
  Purchase #6 $49.75   8.840%   $54.1479   $54.15   $54.15   $54.10  
  Purchase #7 $63.92   12.270%   $71.763   $71.76   $71.75   $71.80  
  7 purchase totals = $822.03       $893.9896   $894.00   $893.95   $893.90