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 $222.59   11.673%   $248.5729   $248.57   $248.55   $248.60  
  Purchase #2 $186.72   13.365%   $211.6751   $211.68   $211.70   $211.70  
  Purchase #3 $214.43   8.256%   $232.1333   $232.13   $232.15   $232.10  
  Purchase #4 $70.70   9.809%   $77.635   $77.64   $77.65   $77.60  
  Purchase #5 $17.70   7.535%   $19.0337   $19.03   $19.05   $19.00  
  Purchase #6 $179.56   12.388%   $201.8039   $201.80   $201.80   $201.80  
  Purchase #7 $235.70   7.781%   $254.0398   $254.04   $254.05   $254.00  
  7 purchase totals = $1,127.40       $1,244.8937   $1,244.89   $1,244.95   $1,244.80