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 $246.89   12.459%   $277.65   $277.65   $277.65   $277.70  
  Purchase #2 $80.41   8.670%   $87.3815   $87.38   $87.40   $87.40  
  Purchase #3 $95.87   7.492%   $103.0526   $103.05   $103.05   $103.10  
  Purchase #4 $20.91   11.379%   $23.2893   $23.29   $23.30   $23.30  
  Purchase #5 $182.96   6.795%   $195.3921   $195.39   $195.40   $195.40  
  Purchase #6 $76.61   8.656%   $83.2414   $83.24   $83.25   $83.20  
  Purchase #7 $243.98   4.873%   $255.8691   $255.87   $255.85   $255.90  
  7 purchase totals = $947.63       $1,025.8760   $1,025.87   $1,025.90   $1,026.00