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 $74.57   5.493%   $78.6661   $78.67   $78.65   $78.70  
  Purchase #2 $87.29   8.219%   $94.4644   $94.46   $94.45   $94.50  
  Purchase #3 $11.98   6.195%   $12.7222   $12.72   $12.70   $12.70  
  Purchase #4 $178.63   8.504%   $193.8207   $193.82   $193.80   $193.80  
  Purchase #5 $86.37   12.222%   $96.9261   $96.93   $96.95   $96.90  
  Purchase #6 $247.60   11.624%   $276.381   $276.38   $276.40   $276.40  
  Purchase #7 $227.76   13.494%   $258.4939   $258.49   $258.50   $258.50  
  7 purchase totals = $914.20       $1,011.4744   $1,011.47   $1,011.45   $1,011.50