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 $250.43   9.348%   $273.8402   $273.84   $273.85   $273.80  
  Purchase #2 $42.42   9.798%   $46.5763   $46.58   $46.60   $46.60  
  Purchase #3 $89.67   7.855%   $96.7136   $96.71   $96.70   $96.70  
  Purchase #4 $73.69   9.337%   $80.5704   $80.57   $80.55   $80.60  
  Purchase #5 $218.31   12.802%   $246.258   $246.26   $246.25   $246.30  
  Purchase #6 $85.50   12.543%   $96.2243   $96.22   $96.20   $96.20  
  Purchase #7 $197.25   3.776%   $204.6982   $204.70   $204.70   $204.70  
  7 purchase totals = $957.27       $1,044.8810   $1,044.88   $1,044.85   $1,044.90