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 $202.49   8.579%   $219.8616   $219.86   $219.85   $219.90  
  Purchase #2 $53.55   3.296%   $55.315   $55.32   $55.30   $55.30  
  Purchase #3 $188.94   8.495%   $204.9905   $204.99   $205.00   $205.00  
  Purchase #4 $24.72   6.753%   $26.3893   $26.39   $26.40   $26.40  
  Purchase #5 $102.90   8.345%   $111.487   $111.49   $111.50   $111.50  
  Purchase #6 $144.63   10.195%   $159.375   $159.38   $159.40   $159.40  
  Purchase #7 $246.65   7.853%   $266.0194   $266.02   $266.00   $266.00  
  7 purchase totals = $963.88       $1,043.4378   $1,043.45   $1,043.45   $1,043.50