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 $190.47   10.740%   $210.9265   $210.93   $210.95   $210.90  
  Purchase #2 $24.45   6.372%   $26.008   $26.01   $26.00   $26.00  
  Purchase #3 $6.76   12.214%   $7.5857   $7.59   $7.60   $7.60  
  Purchase #4 $151.32   11.845%   $169.2439   $169.24   $169.25   $169.20  
  Purchase #5 $208.26   12.167%   $233.599   $233.60   $233.60   $233.60  
  Purchase #6 $184.34   5.645%   $194.746   $194.75   $194.75   $194.70  
  Purchase #7 $227.75   8.611%   $247.3616   $247.36   $247.35   $247.40  
  7 purchase totals = $993.35       $1,089.4707   $1,089.48   $1,089.50   $1,089.40