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 $56.96   5.312%   $59.9857   $59.99   $60.00   $60.00  
  Purchase #2 $53.35   4.590%   $55.7988   $55.80   $55.80   $55.80  
  Purchase #3 $222.75   8.329%   $241.3028   $241.30   $241.30   $241.30  
  Purchase #4 $186.88   3.240%   $192.9349   $192.93   $192.95   $192.90  
  Purchase #5 $237.42   13.266%   $268.9161   $268.92   $268.90   $268.90  
  Purchase #6 $174.69   3.104%   $180.1124   $180.11   $180.10   $180.10  
  Purchase #7 $179.34   12.696%   $202.109   $202.11   $202.10   $202.10  
  7 purchase totals = $1,111.39       $1,201.1597   $1,201.16   $1,201.15   $1,201.10