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 $91.61   5.472%   $96.6229   $96.62   $96.60   $96.60  
  Purchase #2 $161.99   10.867%   $179.5935   $179.59   $179.60   $179.60  
  Purchase #3 $181.73   11.395%   $202.4381   $202.44   $202.45   $202.40  
  Purchase #4 $74.82   8.276%   $81.0121   $81.01   $81.00   $81.00  
  Purchase #5 $195.79   11.438%   $218.1845   $218.18   $218.20   $218.20  
  Purchase #6 $211.25   13.571%   $239.9187   $239.92   $239.90   $239.90  
  Purchase #7 $77.81   6.422%   $82.807   $82.81   $82.80   $82.80  
  7 purchase totals = $995.00       $1,100.5768   $1,100.57   $1,100.55   $1,100.50