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 $148.31   5.793%   $156.9016   $156.90   $156.90   $156.90  
  Purchase #2 $112.81   4.576%   $117.9722   $117.97   $117.95   $118.00  
  Purchase #3 $10.66   5.787%   $11.2769   $11.28   $11.30   $11.30  
  Purchase #4 $232.70   5.624%   $245.787   $245.79   $245.80   $245.80  
  Purchase #5 $53.82   8.140%   $58.2009   $58.20   $58.20   $58.20  
  Purchase #6 $21.72   11.867%   $24.2975   $24.30   $24.30   $24.30  
  Purchase #7 $138.28   10.320%   $152.5505   $152.55   $152.55   $152.60  
  7 purchase totals = $718.30       $766.9866   $766.99   $767.00   $767.10