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 $68.55   11.182%   $76.2153   $76.22   $76.20   $76.20  
  Purchase #2 $228.90   6.499%   $243.7762   $243.78   $243.80   $243.80  
  Purchase #3 $195.74   4.717%   $204.9731   $204.97   $204.95   $205.00  
  Purchase #4 $30.89   11.166%   $34.3392   $34.34   $34.35   $34.30  
  Purchase #5 $174.73   6.138%   $185.4549   $185.45   $185.45   $185.50  
  Purchase #6 $169.96   6.723%   $181.3864   $181.39   $181.40   $181.40  
  Purchase #7 $69.76   13.603%   $79.2495   $79.25   $79.25   $79.20  
  7 purchase totals = $938.53       $1,005.3946   $1,005.40   $1,005.40   $1,005.40