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 $227.33   6.858%   $242.9203   $242.92   $242.90   $242.90  
  Purchase #2 $104.35   5.130%   $109.7032   $109.70   $109.70   $109.70  
  Purchase #3 $165.64   3.294%   $171.0962   $171.10   $171.10   $171.10  
  Purchase #4 $15.53   12.704%   $17.5029   $17.50   $17.50   $17.50  
  Purchase #5 $182.90   10.601%   $202.2892   $202.29   $202.30   $202.30  
  Purchase #6 $205.72   9.264%   $224.7779   $224.78   $224.80   $224.80  
  Purchase #7 $87.31   12.165%   $97.9313   $97.93   $97.95   $97.90  
  7 purchase totals = $988.78       $1,066.2210   $1,066.22   $1,066.25   $1,066.20