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 $230.79   5.751%   $244.0627   $244.06   $244.05   $244.10  
  Purchase #2 $118.90   6.743%   $126.9174   $126.92   $126.90   $126.90  
  Purchase #3 $158.92   9.726%   $174.3766   $174.38   $174.40   $174.40  
  Purchase #4 $151.52   8.793%   $164.8432   $164.84   $164.85   $164.80  
  Purchase #5 $163.90   9.507%   $179.482   $179.48   $179.50   $179.50  
  Purchase #6 $109.76   10.636%   $121.4341   $121.43   $121.45   $121.40  
  Purchase #7 $12.81   5.798%   $13.5527   $13.55   $13.55   $13.60  
  7 purchase totals = $946.60       $1,024.6687   $1,024.66   $1,024.70   $1,024.70