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 $144.82   5.179%   $152.3202   $152.32   $152.30   $152.30  
  Purchase #2 $40.80   11.789%   $45.6099   $45.61   $45.60   $45.60  
  Purchase #3 $17.31   12.692%   $19.507   $19.51   $19.50   $19.50  
  Purchase #4 $238.55   12.358%   $268.03   $268.03   $268.05   $268.00  
  Purchase #5 $119.66   11.464%   $133.3778   $133.38   $133.40   $133.40  
  Purchase #6 $97.75   9.518%   $107.0538   $107.05   $107.05   $107.10  
  Purchase #7 $44.26   10.565%   $48.9361   $48.94   $48.95   $48.90  
  7 purchase totals = $703.15       $774.8348   $774.84   $774.85   $774.80