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 $245.41   11.535%   $273.718   $273.72   $273.70   $273.70  
  Purchase #2 $87.29   4.612%   $91.3158   $91.32   $91.30   $91.30  
  Purchase #3 $116.61   6.397%   $124.0695   $124.07   $124.05   $124.10  
  Purchase #4 $212.63   12.673%   $239.5766   $239.58   $239.60   $239.60  
  Purchase #5 $210.63   3.423%   $217.8399   $217.84   $217.85   $217.80  
  Purchase #6 $8.27   4.577%   $8.6485   $8.65   $8.65   $8.60  
  Purchase #7 $138.88   11.795%   $155.2609   $155.26   $155.25   $155.30  
  7 purchase totals = $1,019.72       $1,110.4292   $1,110.44   $1,110.40   $1,110.40