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 $129.76   9.449%   $142.021   $142.02   $142.00   $142.00  
  Purchase #2 $70.84   7.207%   $75.9454   $75.95   $75.95   $75.90  
  Purchase #3 $92.71   6.120%   $98.3839   $98.38   $98.40   $98.40  
  Purchase #4 $99.91   3.620%   $103.5267   $103.53   $103.55   $103.50  
  Purchase #5 $178.95   13.651%   $203.3785   $203.38   $203.40   $203.40  
  Purchase #6 $19.44   3.582%   $20.1363   $20.14   $20.15   $20.10  
  Purchase #7 $46.28   13.779%   $52.6569   $52.66   $52.65   $52.70  
  7 purchase totals = $637.89       $696.0487   $696.06   $696.10   $696.00