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 $148.37   7.369%   $159.3034   $159.30   $159.30   $159.30  
  Purchase #2 $61.91   6.369%   $65.853   $65.85   $65.85   $65.90  
  Purchase #3 $15.29   13.189%   $17.3066   $17.31   $17.30   $17.30  
  Purchase #4 $188.55   7.387%   $202.4782   $202.48   $202.50   $202.50  
  Purchase #5 $71.27   10.243%   $78.5702   $78.57   $78.55   $78.60  
  Purchase #6 $202.25   11.841%   $226.1984   $226.20   $226.20   $226.20  
  Purchase #7 $236.69   12.270%   $265.7319   $265.73   $265.75   $265.70  
  7 purchase totals = $924.33       $1,015.4417   $1,015.44   $1,015.45   $1,015.50