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 $226.29   5.770%   $239.3469   $239.35   $239.35   $239.30  
  Purchase #2 $160.47   5.709%   $169.6312   $169.63   $169.65   $169.60  
  Purchase #3 $159.30   5.670%   $168.3323   $168.33   $168.35   $168.30  
  Purchase #4 $50.96   11.257%   $56.6966   $56.70   $56.70   $56.70  
  Purchase #5 $217.29   7.433%   $233.4412   $233.44   $233.45   $233.40  
  Purchase #6 $238.91   13.674%   $271.5786   $271.58   $271.60   $271.60  
  Purchase #7 $48.81   9.192%   $53.2966   $53.30   $53.30   $53.30  
  7 purchase totals = $1,102.03       $1,192.3234   $1,192.33   $1,192.40   $1,192.20