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 $250.97   5.539%   $264.8712   $264.87   $264.85   $264.90  
  Purchase #2 $67.59   8.691%   $73.4642   $73.46   $73.45   $73.50  
  Purchase #3 $232.57   3.347%   $240.3541   $240.35   $240.35   $240.40  
  Purchase #4 $210.97   6.763%   $225.2379   $225.24   $225.25   $225.20  
  Purchase #5 $218.67   3.641%   $226.6318   $226.63   $226.65   $226.60  
  Purchase #6 $147.83   5.616%   $156.1321   $156.13   $156.15   $156.10  
  Purchase #7 $50.46   9.486%   $55.2466   $55.25   $55.25   $55.20  
  7 purchase totals = $1,179.06       $1,241.9379   $1,241.93   $1,241.95   $1,241.90