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 $51.61   5.341%   $54.3665   $54.37   $54.35   $54.40  
  Purchase #2 $195.28   3.863%   $202.8237   $202.82   $202.80   $202.80  
  Purchase #3 $99.97   3.343%   $103.312   $103.31   $103.30   $103.30  
  Purchase #4 $154.26   13.395%   $174.9231   $174.92   $174.90   $174.90  
  Purchase #5 $246.38   3.246%   $254.3775   $254.38   $254.40   $254.40  
  Purchase #6 $226.78   7.816%   $244.5051   $244.51   $244.50   $244.50  
  Purchase #7 $11.46   13.396%   $12.9952   $13.00   $13.00   $13.00  
  7 purchase totals = $985.74       $1,047.3031   $1,047.31   $1,047.25   $1,047.30