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 $164.54   8.766%   $178.9636   $178.96   $178.95   $179.00  
  Purchase #2 $186.73   10.840%   $206.9715   $206.97   $206.95   $207.00  
  Purchase #3 $179.72   8.339%   $194.7069   $194.71   $194.70   $194.70  
  Purchase #4 $24.64   9.502%   $26.9813   $26.98   $27.00   $27.00  
  Purchase #5 $172.43   6.695%   $183.9742   $183.97   $183.95   $184.00  
  Purchase #6 $239.33   4.702%   $250.5833   $250.58   $250.60   $250.60  
  Purchase #7 $176.33   5.551%   $186.1181   $186.12   $186.10   $186.10  
  7 purchase totals = $1,143.72       $1,228.2989   $1,228.29   $1,228.25   $1,228.40