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 $178.38   8.387%   $193.3407   $193.34   $193.35   $193.30  
  Purchase #2 $236.90   4.843%   $248.3731   $248.37   $248.35   $248.40  
  Purchase #3 $218.27   13.394%   $247.5051   $247.51   $247.50   $247.50  
  Purchase #4 $69.99   8.181%   $75.7159   $75.72   $75.70   $75.70  
  Purchase #5 $192.57   13.734%   $219.0176   $219.02   $219.00   $219.00  
  Purchase #6 $119.31   4.516%   $124.698   $124.70   $124.70   $124.70  
  Purchase #7 $45.96   3.561%   $47.5966   $47.60   $47.60   $47.60  
  7 purchase totals = $1,061.38       $1,156.2470   $1,156.26   $1,156.20   $1,156.20