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 $244.66   5.414%   $257.9059   $257.91   $257.90   $257.90  
  Purchase #2 $170.93   4.349%   $178.3637   $178.36   $178.35   $178.40  
  Purchase #3 $22.32   3.641%   $23.1327   $23.13   $23.15   $23.10  
  Purchase #4 $200.41   6.112%   $212.6591   $212.66   $212.65   $212.70  
  Purchase #5 $50.70   12.825%   $57.2023   $57.20   $57.20   $57.20  
  Purchase #6 $239.93   3.267%   $247.7685   $247.77   $247.75   $247.80  
  Purchase #7 $123.72   8.779%   $134.5814   $134.58   $134.60   $134.60  
  7 purchase totals = $1,052.67       $1,111.6136   $1,111.61   $1,111.60   $1,111.70