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 $110.92   10.247%   $122.286   $122.29   $122.30   $122.30  
  Purchase #2 $117.38   13.536%   $133.2686   $133.27   $133.25   $133.30  
  Purchase #3 $43.68   12.246%   $49.0291   $49.03   $49.05   $49.00  
  Purchase #4 $180.72   12.306%   $202.9594   $202.96   $202.95   $203.00  
  Purchase #5 $199.30   13.860%   $226.923   $226.92   $226.90   $226.90  
  Purchase #6 $65.57   12.784%   $73.9525   $73.95   $73.95   $74.00  
  Purchase #7 $36.68   13.249%   $41.5397   $41.54   $41.55   $41.50  
  7 purchase totals = $754.25       $849.9583   $849.96   $849.95   $850.00