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 $153.42   8.535%   $166.5144   $166.51   $166.50   $166.50  
  Purchase #2 $220.68   6.782%   $235.6465   $235.65   $235.65   $235.60  
  Purchase #3 $179.98   7.744%   $193.9177   $193.92   $193.90   $193.90  
  Purchase #4 $45.55   4.148%   $47.4394   $47.44   $47.45   $47.40  
  Purchase #5 $118.81   10.805%   $131.6474   $131.65   $131.65   $131.60  
  Purchase #6 $141.32   3.771%   $146.6492   $146.65   $146.65   $146.60  
  Purchase #7 $82.68   3.366%   $85.463   $85.46   $85.45   $85.50  
  7 purchase totals = $942.44       $1,007.2776   $1,007.28   $1,007.25   $1,007.10