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 $85.69   6.635%   $91.3755   $91.38   $91.40   $91.40  
  Purchase #2 $204.97   11.832%   $229.2221   $229.22   $229.20   $229.20  
  Purchase #3 $54.98   8.429%   $59.6143   $59.61   $59.60   $59.60  
  Purchase #4 $78.31   10.869%   $86.8215   $86.82   $86.80   $86.80  
  Purchase #5 $236.95   8.561%   $257.2353   $257.24   $257.25   $257.20  
  Purchase #6 $245.41   6.285%   $260.834   $260.83   $260.85   $260.80  
  Purchase #7 $81.74   3.475%   $84.5805   $84.58   $84.60   $84.60  
  7 purchase totals = $988.05       $1,069.6832   $1,069.68   $1,069.70   $1,069.60