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 $206.91   5.369%   $218.019   $218.02   $218.00   $218.00  
  Purchase #2 $49.64   8.637%   $53.9274   $53.93   $53.95   $53.90  
  Purchase #3 $156.78   8.774%   $170.5359   $170.54   $170.55   $170.50  
  Purchase #4 $115.39   12.164%   $129.426   $129.43   $129.45   $129.40  
  Purchase #5 $241.78   3.540%   $250.339   $250.34   $250.35   $250.30  
  Purchase #6 $152.77   3.846%   $158.6455   $158.65   $158.65   $158.60  
  Purchase #7 $26.83   4.203%   $27.9577   $27.96   $27.95   $28.00  
  7 purchase totals = $950.10       $1,008.8505   $1,008.87   $1,008.90   $1,008.70