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 $103.82   13.851%   $118.2001   $118.20   $118.20   $118.20  
  Purchase #2 $119.92   12.230%   $134.5862   $134.59   $134.60   $134.60  
  Purchase #3 $133.47   4.409%   $139.3547   $139.35   $139.35   $139.40  
  Purchase #4 $246.84   4.487%   $257.9157   $257.92   $257.90   $257.90  
  Purchase #5 $71.56   8.757%   $77.8265   $77.83   $77.85   $77.80  
  Purchase #6 $37.93   8.706%   $41.2322   $41.23   $41.25   $41.20  
  Purchase #7 $227.54   11.801%   $254.392   $254.39   $254.40   $254.40  
  7 purchase totals = $941.08       $1,023.5074   $1,023.51   $1,023.55   $1,023.50