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 $211.61   11.502%   $235.9494   $235.95   $235.95   $235.90  
  Purchase #2 $76.99   11.783%   $86.0617   $86.06   $86.05   $86.10  
  Purchase #3 $76.61   5.455%   $80.7891   $80.79   $80.80   $80.80  
  Purchase #4 $220.44   3.704%   $228.6051   $228.61   $228.60   $228.60  
  Purchase #5 $250.67   8.819%   $272.7766   $272.78   $272.80   $272.80  
  Purchase #6 $105.54   13.315%   $119.5927   $119.59   $119.60   $119.60  
  Purchase #7 $216.42   4.781%   $226.767   $226.77   $226.75   $226.80  
  7 purchase totals = $1,158.28       $1,250.5416   $1,250.55   $1,250.55   $1,250.60