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 $86.32   10.673%   $95.5329   $95.53   $95.55   $95.50  
  Purchase #2 $189.89   7.597%   $204.3159   $204.32   $204.30   $204.30  
  Purchase #3 $243.87   3.699%   $252.8908   $252.89   $252.90   $252.90  
  Purchase #4 $208.50   13.119%   $235.8531   $235.85   $235.85   $235.90  
  Purchase #5 $207.70   8.779%   $225.934   $225.93   $225.95   $225.90  
  Purchase #6 $210.37   5.796%   $222.563   $222.56   $222.55   $222.60  
  Purchase #7 $39.48   5.321%   $41.5807   $41.58   $41.60   $41.60  
  7 purchase totals = $1,186.13       $1,278.6704   $1,278.66   $1,278.70   $1,278.70