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 $51.76   8.389%   $56.1021   $56.10   $56.10   $56.10  
  Purchase #2 $159.72   11.808%   $178.5797   $178.58   $178.60   $178.60  
  Purchase #3 $153.58   13.319%   $174.0353   $174.04   $174.05   $174.00  
  Purchase #4 $226.85   7.743%   $244.415   $244.42   $244.40   $244.40  
  Purchase #5 $249.82   7.849%   $269.4284   $269.43   $269.45   $269.40  
  Purchase #6 $188.76   12.116%   $211.6302   $211.63   $211.65   $211.60  
  Purchase #7 $116.73   8.689%   $126.8727   $126.87   $126.85   $126.90  
  7 purchase totals = $1,147.22       $1,261.0634   $1,261.07   $1,261.10   $1,261.00