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 $43.45   3.173%   $44.8287   $44.83   $44.85   $44.80  
  Purchase #2 $214.76   12.619%   $241.8606   $241.86   $241.85   $241.90  
  Purchase #3 $153.86   5.208%   $161.873   $161.87   $161.85   $161.90  
  Purchase #4 $201.36   5.707%   $212.8516   $212.85   $212.85   $212.90  
  Purchase #5 $177.78   13.433%   $201.6612   $201.66   $201.65   $201.70  
  Purchase #6 $159.97   10.260%   $176.3829   $176.38   $176.40   $176.40  
  Purchase #7 $27.55   3.563%   $28.5316   $28.53   $28.55   $28.50  
  7 purchase totals = $978.73       $1,067.9896   $1,067.98   $1,068.00   $1,068.10