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 $246.96   5.189%   $259.7748   $259.77   $259.75   $259.80  
  Purchase #2 $225.67   11.873%   $252.4638   $252.46   $252.45   $252.50  
  Purchase #3 $49.33   9.527%   $54.0297   $54.03   $54.05   $54.00  
  Purchase #4 $203.90   13.543%   $231.5142   $231.51   $231.50   $231.50  
  Purchase #5 $101.54   13.696%   $115.4469   $115.45   $115.45   $115.40  
  Purchase #6 $93.87   5.714%   $99.2337   $99.23   $99.25   $99.20  
  Purchase #7 $110.41   6.802%   $117.9201   $117.92   $117.90   $117.90  
  7 purchase totals = $1,031.68       $1,130.3832   $1,130.37   $1,130.35   $1,130.30