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 $168.91   8.145%   $182.6677   $182.67   $182.65   $182.70  
  Purchase #2 $22.68   13.318%   $25.7005   $25.70   $25.70   $25.70  
  Purchase #3 $66.85   3.130%   $68.9424   $68.94   $68.95   $68.90  
  Purchase #4 $198.81   12.424%   $223.5102   $223.51   $223.50   $223.50  
  Purchase #5 $123.92   5.145%   $130.2957   $130.30   $130.30   $130.30  
  Purchase #6 $222.55   7.284%   $238.7605   $238.76   $238.75   $238.80  
  Purchase #7 $165.90   5.641%   $175.2584   $175.26   $175.25   $175.30  
  7 purchase totals = $969.62       $1,045.1354   $1,045.14   $1,045.10   $1,045.20