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 $86.72   11.589%   $96.77   $96.77   $96.75   $96.80  
  Purchase #2 $162.73   8.314%   $176.2594   $176.26   $176.25   $176.30  
  Purchase #3 $44.51   9.459%   $48.7202   $48.72   $48.70   $48.70  
  Purchase #4 $135.29   5.529%   $142.7702   $142.77   $142.75   $142.80  
  Purchase #5 $228.81   12.123%   $256.5486   $256.55   $256.55   $256.50  
  Purchase #6 $200.50   8.568%   $217.6788   $217.68   $217.70   $217.70  
  Purchase #7 $182.31   5.377%   $192.1128   $192.11   $192.10   $192.10  
  7 purchase totals = $1,040.87       $1,130.8600   $1,130.86   $1,130.80   $1,130.90