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 $161.97   4.614%   $169.4433   $169.44   $169.45   $169.40  
  Purchase #2 $198.70   9.386%   $217.35   $217.35   $217.35   $217.40  
  Purchase #3 $165.56   4.805%   $173.5152   $173.52   $173.50   $173.50  
  Purchase #4 $32.38   7.449%   $34.792   $34.79   $34.80   $34.80  
  Purchase #5 $132.48   3.213%   $136.7366   $136.74   $136.75   $136.70  
  Purchase #6 $115.62   11.440%   $128.8469   $128.85   $128.85   $128.80  
  Purchase #7 $250.28   9.833%   $274.89   $274.89   $274.90   $274.90  
  7 purchase totals = $1,056.99       $1,135.5740   $1,135.58   $1,135.60   $1,135.50