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 $232.42   9.611%   $254.7579   $254.76   $254.75   $254.80  
  Purchase #2 $87.65   11.732%   $97.9331   $97.93   $97.95   $97.90  
  Purchase #3 $11.70   12.102%   $13.1159   $13.12   $13.10   $13.10  
  Purchase #4 $216.92   11.176%   $241.163   $241.16   $241.15   $241.20  
  Purchase #5 $198.49   11.126%   $220.574   $220.57   $220.55   $220.60  
  Purchase #6 $72.50   12.104%   $81.2754   $81.28   $81.30   $81.30  
  Purchase #7 $146.44   10.778%   $162.2233   $162.22   $162.20   $162.20  
  7 purchase totals = $966.12       $1,071.0426   $1,071.04   $1,071.00   $1,071.10