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 $205.73   10.238%   $226.7926   $226.79   $226.80   $226.80  
  Purchase #2 $23.75   13.128%   $26.8679   $26.87   $26.85   $26.90  
  Purchase #3 $56.72   5.557%   $59.8719   $59.87   $59.85   $59.90  
  Purchase #4 $131.84   3.515%   $136.4742   $136.47   $136.45   $136.50  
  Purchase #5 $185.39   10.528%   $204.9079   $204.91   $204.90   $204.90  
  Purchase #6 $207.57   4.813%   $217.5603   $217.56   $217.55   $217.60  
  Purchase #7 $80.47   8.593%   $87.3848   $87.38   $87.40   $87.40  
  7 purchase totals = $891.47       $959.8596   $959.85   $959.80   $960.00