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 $25.98   3.829%   $26.9748   $26.97   $26.95   $27.00  
  Purchase #2 $168.79   13.779%   $192.0476   $192.05   $192.05   $192.00  
  Purchase #3 $134.98   8.651%   $146.6571   $146.66   $146.65   $146.70  
  Purchase #4 $247.51   3.379%   $255.8734   $255.87   $255.85   $255.90  
  Purchase #5 $98.78   8.564%   $107.2395   $107.24   $107.25   $107.20  
  Purchase #6 $137.47   8.612%   $149.3089   $149.31   $149.30   $149.30  
  Purchase #7 $116.83   5.734%   $123.529   $123.53   $123.55   $123.50  
  7 purchase totals = $930.34       $1,001.6303   $1,001.63   $1,001.60   $1,001.60