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 $240.51   12.150%   $269.732   $269.73   $269.75   $269.70  
  Purchase #2 $23.65   8.563%   $25.6751   $25.68   $25.70   $25.70  
  Purchase #3 $34.85   10.798%   $38.6131   $38.61   $38.60   $38.60  
  Purchase #4 $160.48   9.807%   $176.2183   $176.22   $176.20   $176.20  
  Purchase #5 $178.47   3.380%   $184.5023   $184.50   $184.50   $184.50  
  Purchase #6 $229.39   6.696%   $244.75   $244.75   $244.75   $244.80  
  Purchase #7 $74.35   12.351%   $83.533   $83.53   $83.55   $83.50  
  7 purchase totals = $941.70       $1,023.0238   $1,023.02   $1,023.05   $1,023.00