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 $53.74   4.818%   $56.3292   $56.33   $56.35   $56.30  
  Purchase #2 $202.83   5.183%   $213.3427   $213.34   $213.35   $213.30  
  Purchase #3 $125.39   9.821%   $137.7046   $137.70   $137.70   $137.70  
  Purchase #4 $224.53   8.170%   $242.8741   $242.87   $242.85   $242.90  
  Purchase #5 $167.29   7.266%   $179.4453   $179.45   $179.45   $179.40  
  Purchase #6 $16.73   5.436%   $17.6394   $17.64   $17.65   $17.60  
  Purchase #7 $227.50   11.138%   $252.839   $252.84   $252.85   $252.80  
  7 purchase totals = $1,018.01       $1,100.1743   $1,100.17   $1,100.20   $1,100.00