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 $92.45   12.116%   $103.6512   $103.65   $103.65   $103.70  
  Purchase #2 $186.25   8.804%   $202.6475   $202.65   $202.65   $202.60  
  Purchase #3 $42.67   7.242%   $45.7602   $45.76   $45.75   $45.80  
  Purchase #4 $111.76   13.243%   $126.5604   $126.56   $126.55   $126.60  
  Purchase #5 $148.97   3.545%   $154.251   $154.25   $154.25   $154.30  
  Purchase #6 $31.69   13.760%   $36.0505   $36.05   $36.05   $36.10  
  Purchase #7 $90.45   4.378%   $94.4099   $94.41   $94.40   $94.40  
  7 purchase totals = $704.24       $763.3307   $763.33   $763.30   $763.50