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 $54.33   12.829%   $61.3   $61.30   $61.30   $61.30  
  Purchase #2 $74.59   9.258%   $81.4955   $81.50   $81.50   $81.50  
  Purchase #3 $64.55   8.228%   $69.8612   $69.86   $69.85   $69.90  
  Purchase #4 $193.65   5.649%   $204.5893   $204.59   $204.60   $204.60  
  Purchase #5 $247.60   7.333%   $265.7565   $265.76   $265.75   $265.80  
  Purchase #6 $72.61   13.389%   $82.3318   $82.33   $82.35   $82.30  
  Purchase #7 $15.48   8.161%   $16.7433   $16.74   $16.75   $16.70  
  7 purchase totals = $722.81       $782.0776   $782.08   $782.10   $782.10