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 $148.81   12.721%   $167.7401   $167.74   $167.75   $167.70  
  Purchase #2 $141.55   5.644%   $149.5391   $149.54   $149.55   $149.50  
  Purchase #3 $66.38   11.320%   $73.8942   $73.89   $73.90   $73.90  
  Purchase #4 $169.92   9.447%   $185.9723   $185.97   $185.95   $186.00  
  Purchase #5 $111.36   11.171%   $123.8   $123.80   $123.80   $123.80  
  Purchase #6 $192.60   9.627%   $211.1416   $211.14   $211.15   $211.10  
  Purchase #7 $76.33   10.588%   $84.4118   $84.41   $84.40   $84.40  
  7 purchase totals = $906.95       $996.4991   $996.49   $996.50   $996.40