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 $165.33   6.182%   $175.5507   $175.55   $175.55   $175.60  
  Purchase #2 $95.93   12.432%   $107.856   $107.86   $107.85   $107.90  
  Purchase #3 $201.71   3.751%   $209.2761   $209.28   $209.30   $209.30  
  Purchase #4 $124.99   4.285%   $130.3458   $130.35   $130.35   $130.30  
  Purchase #5 $241.44   7.126%   $258.645   $258.65   $258.65   $258.60  
  Purchase #6 $166.78   6.484%   $177.594   $177.59   $177.60   $177.60  
  Purchase #7 $117.30   6.289%   $124.677   $124.68   $124.70   $124.70  
  7 purchase totals = $1,113.48       $1,183.9446   $1,183.96   $1,184.00   $1,184.00