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 $61.98   13.392%   $70.2804   $70.28   $70.30   $70.30  
  Purchase #2 $23.26   10.440%   $25.6883   $25.69   $25.70   $25.70  
  Purchase #3 $209.94   3.650%   $217.6028   $217.60   $217.60   $217.60  
  Purchase #4 $20.45   9.560%   $22.405   $22.41   $22.40   $22.40  
  Purchase #5 $245.66   10.398%   $271.2037   $271.20   $271.20   $271.20  
  Purchase #6 $192.57   8.372%   $208.692   $208.69   $208.70   $208.70  
  Purchase #7 $206.68   4.780%   $216.5593   $216.56   $216.55   $216.60  
  7 purchase totals = $960.54       $1,032.4315   $1,032.43   $1,032.45   $1,032.50