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 $248.74   8.467%   $269.8008   $269.80   $269.80   $269.80  
  Purchase #2 $137.62   11.292%   $153.1601   $153.16   $153.15   $153.20  
  Purchase #3 $174.52   13.226%   $197.602   $197.60   $197.60   $197.60  
  Purchase #4 $180.40   13.197%   $204.2074   $204.21   $204.20   $204.20  
  Purchase #5 $29.94   4.135%   $31.178   $31.18   $31.20   $31.20  
  Purchase #6 $179.76   11.686%   $200.7668   $200.77   $200.75   $200.80  
  Purchase #7 $178.66   5.734%   $188.9044   $188.90   $188.90   $188.90  
  7 purchase totals = $1,129.64       $1,245.6195   $1,245.62   $1,245.60   $1,245.70