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 $183.82   11.715%   $205.3545   $205.35   $205.35   $205.40  
  Purchase #2 $244.95   9.389%   $267.9484   $267.95   $267.95   $267.90  
  Purchase #3 $140.89   3.196%   $145.3928   $145.39   $145.40   $145.40  
  Purchase #4 $89.73   9.748%   $98.4769   $98.48   $98.50   $98.50  
  Purchase #5 $220.62   12.291%   $247.7364   $247.74   $247.75   $247.70  
  Purchase #6 $175.79   5.362%   $185.2159   $185.22   $185.20   $185.20  
  Purchase #7 $184.46   10.255%   $203.3764   $203.38   $203.40   $203.40  
  7 purchase totals = $1,240.26       $1,353.5013   $1,353.51   $1,353.55   $1,353.50