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 $48.66   10.157%   $53.6024   $53.60   $53.60   $53.60  
  Purchase #2 $70.61   7.182%   $75.6812   $75.68   $75.70   $75.70  
  Purchase #3 $139.29   5.276%   $146.6389   $146.64   $146.65   $146.60  
  Purchase #4 $198.58   4.841%   $208.1933   $208.19   $208.20   $208.20  
  Purchase #5 $127.87   6.636%   $136.3555   $136.36   $136.35   $136.40  
  Purchase #6 $154.77   11.444%   $172.4819   $172.48   $172.50   $172.50  
  Purchase #7 $201.91   8.267%   $218.6019   $218.60   $218.60   $218.60  
  7 purchase totals = $941.69       $1,011.5551   $1,011.55   $1,011.60   $1,011.60