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 $156.86   7.744%   $169.0072   $169.01   $169.00   $169.00  
  Purchase #2 $206.65   11.267%   $229.9333   $229.93   $229.95   $229.90  
  Purchase #3 $97.36   6.367%   $103.5589   $103.56   $103.55   $103.60  
  Purchase #4 $173.93   10.386%   $191.9944   $191.99   $192.00   $192.00  
  Purchase #5 $41.31   12.548%   $46.4936   $46.49   $46.50   $46.50  
  Purchase #6 $43.95   7.463%   $47.23   $47.23   $47.25   $47.20  
  Purchase #7 $239.52   13.150%   $271.0169   $271.02   $271.00   $271.00  
  7 purchase totals = $959.58       $1,059.2343   $1,059.23   $1,059.25   $1,059.20