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 $114.81   5.656%   $121.3037   $121.30   $121.30   $121.30  
  Purchase #2 $231.41   13.801%   $263.3469   $263.35   $263.35   $263.30  
  Purchase #3 $13.99   6.624%   $14.9167   $14.92   $14.90   $14.90  
  Purchase #4 $53.97   5.190%   $56.771   $56.77   $56.75   $56.80  
  Purchase #5 $46.66   5.853%   $49.391   $49.39   $49.40   $49.40  
  Purchase #6 $115.41   9.190%   $126.0162   $126.02   $126.00   $126.00  
  Purchase #7 $169.44   9.375%   $185.325   $185.33   $185.35   $185.30  
  7 purchase totals = $745.69       $817.0705   $817.08   $817.05   $817.00