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 $192.97   6.339%   $205.2024   $205.20   $205.20   $205.20  
  Purchase #2 $214.72   13.868%   $244.4974   $244.50   $244.50   $244.50  
  Purchase #3 $85.47   8.120%   $92.4102   $92.41   $92.40   $92.40  
  Purchase #4 $58.30   11.258%   $64.8634   $64.86   $64.85   $64.90  
  Purchase #5 $97.55   11.736%   $108.9985   $109.00   $109.00   $109.00  
  Purchase #6 $181.33   6.363%   $192.868   $192.87   $192.85   $192.90  
  Purchase #7 $97.39   6.114%   $103.3444   $103.34   $103.35   $103.30  
  7 purchase totals = $927.73       $1,012.1843   $1,012.18   $1,012.15   $1,012.20