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 $169.76   10.354%   $187.337   $187.34   $187.35   $187.30  
  Purchase #2 $224.67   7.536%   $241.6011   $241.60   $241.60   $241.60  
  Purchase #3 $153.64   10.604%   $169.932   $169.93   $169.95   $169.90  
  Purchase #4 $246.56   11.125%   $273.9898   $273.99   $274.00   $274.00  
  Purchase #5 $202.99   11.825%   $226.9936   $226.99   $227.00   $227.00  
  Purchase #6 $136.51   11.774%   $152.5827   $152.58   $152.60   $152.60  
  Purchase #7 $77.97   12.464%   $87.6882   $87.69   $87.70   $87.70  
  7 purchase totals = $1,212.10       $1,340.1244   $1,340.12   $1,340.20   $1,340.10