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 $101.45   6.402%   $107.9448   $107.94   $107.95   $107.90  
  Purchase #2 $221.85   10.144%   $244.3545   $244.35   $244.35   $244.40  
  Purchase #3 $201.89   7.126%   $216.2767   $216.28   $216.30   $216.30  
  Purchase #4 $125.66   6.236%   $133.4962   $133.50   $133.50   $133.50  
  Purchase #5 $31.83   8.617%   $34.5728   $34.57   $34.55   $34.60  
  Purchase #6 $118.94   12.656%   $133.993   $133.99   $134.00   $134.00  
  Purchase #7 $143.44   6.707%   $153.0605   $153.06   $153.05   $153.10  
  7 purchase totals = $945.06       $1,023.6985   $1,023.69   $1,023.70   $1,023.80