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 $163.79   12.412%   $184.1196   $184.12   $184.10   $184.10  
  Purchase #2 $57.28   4.495%   $59.8547   $59.85   $59.85   $59.90  
  Purchase #3 $129.80   6.546%   $138.2967   $138.30   $138.30   $138.30  
  Purchase #4 $216.78   7.252%   $232.5009   $232.50   $232.50   $232.50  
  Purchase #5 $218.87   9.184%   $238.971   $238.97   $238.95   $239.00  
  Purchase #6 $231.84   8.615%   $251.813   $251.81   $251.80   $251.80  
  Purchase #7 $242.81   4.766%   $254.3823   $254.38   $254.40   $254.40  
  7 purchase totals = $1,261.17       $1,359.9382   $1,359.93   $1,359.90   $1,360.00