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 $116.29   6.671%   $124.0477   $124.05   $124.05   $124.00  
  Purchase #2 $250.94   4.491%   $262.2097   $262.21   $262.20   $262.20  
  Purchase #3 $191.70   10.682%   $212.1774   $212.18   $212.20   $212.20  
  Purchase #4 $76.75   8.220%   $83.0589   $83.06   $83.05   $83.10  
  Purchase #5 $169.52   7.659%   $182.5035   $182.50   $182.50   $182.50  
  Purchase #6 $211.93   13.584%   $240.7186   $240.72   $240.70   $240.70  
  Purchase #7 $68.60   12.750%   $77.3465   $77.35   $77.35   $77.30  
  7 purchase totals = $1,085.73       $1,182.0623   $1,182.07   $1,182.05   $1,182.00