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 $241.47   9.827%   $265.1993   $265.20   $265.20   $265.20  
  Purchase #2 $85.59   13.644%   $97.2679   $97.27   $97.25   $97.30  
  Purchase #3 $219.84   12.531%   $247.3882   $247.39   $247.40   $247.40  
  Purchase #4 $233.45   8.129%   $252.4272   $252.43   $252.45   $252.40  
  Purchase #5 $73.34   7.190%   $78.6131   $78.61   $78.60   $78.60  
  Purchase #6 $194.65   4.107%   $202.6443   $202.64   $202.65   $202.60  
  Purchase #7 $157.69   6.371%   $167.7364   $167.74   $167.75   $167.70  
  7 purchase totals = $1,206.03       $1,311.2764   $1,311.28   $1,311.30   $1,311.20