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 $164.87   13.395%   $186.9543   $186.95   $186.95   $187.00  
  Purchase #2 $147.57   10.589%   $163.1962   $163.20   $163.20   $163.20  
  Purchase #3 $241.47   13.322%   $273.6386   $273.64   $273.65   $273.60  
  Purchase #4 $209.86   4.817%   $219.969   $219.97   $219.95   $220.00  
  Purchase #5 $176.98   6.625%   $188.7049   $188.70   $188.70   $188.70  
  Purchase #6 $10.55   13.284%   $11.9515   $11.95   $11.95   $12.00  
  Purchase #7 $54.61   5.465%   $57.5944   $57.59   $57.60   $57.60  
  7 purchase totals = $1,005.91       $1,102.0089   $1,102.00   $1,102.00   $1,102.10