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 $228.88   5.183%   $240.7429   $240.74   $240.75   $240.70  
  Purchase #2 $149.59   11.857%   $167.3269   $167.33   $167.35   $167.30  
  Purchase #3 $43.99   8.595%   $47.7709   $47.77   $47.75   $47.80  
  Purchase #4 $237.55   13.436%   $269.4672   $269.47   $269.45   $269.50  
  Purchase #5 $96.73   6.513%   $103.03   $103.03   $103.05   $103.00  
  Purchase #6 $147.73   6.505%   $157.3398   $157.34   $157.35   $157.30  
  Purchase #7 $25.31   4.858%   $26.5396   $26.54   $26.55   $26.50  
  7 purchase totals = $929.78       $1,012.2173   $1,012.22   $1,012.25   $1,012.10