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 $104.58   11.676%   $116.7908   $116.79   $116.80   $116.80  
  Purchase #2 $169.73   8.346%   $183.8957   $183.90   $183.90   $183.90  
  Purchase #3 $91.77   5.342%   $96.6724   $96.67   $96.65   $96.70  
  Purchase #4 $250.81   7.461%   $269.5229   $269.52   $269.50   $269.50  
  Purchase #5 $185.82   3.135%   $191.6455   $191.65   $191.65   $191.60  
  Purchase #6 $174.51   13.262%   $197.6535   $197.65   $197.65   $197.70  
  Purchase #7 $213.43   6.682%   $227.6914   $227.69   $227.70   $227.70  
  7 purchase totals = $1,190.65       $1,283.8722   $1,283.87   $1,283.85   $1,283.90