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 $167.57   9.523%   $183.5277   $183.53   $183.55   $183.50  
  Purchase #2 $164.88   8.133%   $178.2897   $178.29   $178.30   $178.30  
  Purchase #3 $116.34   13.345%   $131.8656   $131.87   $131.85   $131.90  
  Purchase #4 $226.49   9.285%   $247.5196   $247.52   $247.50   $247.50  
  Purchase #5 $103.45   8.634%   $112.3819   $112.38   $112.40   $112.40  
  Purchase #6 $230.52   10.536%   $254.8076   $254.81   $254.80   $254.80  
  Purchase #7 $10.61   6.206%   $11.2685   $11.27   $11.25   $11.30  
  7 purchase totals = $1,019.86       $1,119.6606   $1,119.67   $1,119.65   $1,119.70