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 $48.92   13.823%   $55.6822   $55.68   $55.70   $55.70  
  Purchase #2 $247.53   5.730%   $261.7135   $261.71   $261.70   $261.70  
  Purchase #3 $123.47   6.407%   $131.3807   $131.38   $131.40   $131.40  
  Purchase #4 $123.31   8.490%   $133.779   $133.78   $133.80   $133.80  
  Purchase #5 $201.40   4.758%   $210.9826   $210.98   $211.00   $211.00  
  Purchase #6 $198.80   6.844%   $212.4059   $212.41   $212.40   $212.40  
  Purchase #7 $214.37   4.529%   $224.0788   $224.08   $224.10   $224.10  
  7 purchase totals = $1,157.80       $1,230.0227   $1,230.02   $1,230.10   $1,230.10