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 $248.25   5.352%   $261.5363   $261.54   $261.55   $261.50  
  Purchase #2 $138.42   13.307%   $156.8395   $156.84   $156.85   $156.80  
  Purchase #3 $93.31   3.443%   $96.5227   $96.52   $96.50   $96.50  
  Purchase #4 $140.51   7.856%   $151.5485   $151.55   $151.55   $151.50  
  Purchase #5 $54.59   10.826%   $60.4999   $60.50   $60.50   $60.50  
  Purchase #6 $63.82   8.449%   $69.2122   $69.21   $69.20   $69.20  
  Purchase #7 $164.59   6.803%   $175.7871   $175.79   $175.80   $175.80  
  7 purchase totals = $903.49       $971.9462   $971.95   $971.95   $971.80