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 $48.78   11.747%   $54.5102   $54.51   $54.50   $54.50  
  Purchase #2 $106.79   7.352%   $114.6412   $114.64   $114.65   $114.60  
  Purchase #3 $206.89   8.649%   $224.7839   $224.78   $224.80   $224.80  
  Purchase #4 $143.80   13.204%   $162.7874   $162.79   $162.80   $162.80  
  Purchase #5 $234.73   4.404%   $245.0675   $245.07   $245.05   $245.10  
  Purchase #6 $176.77   4.461%   $184.6557   $184.66   $184.65   $184.70  
  Purchase #7 $216.61   5.774%   $229.1171   $229.12   $229.10   $229.10  
  7 purchase totals = $1,134.37       $1,215.5630   $1,215.57   $1,215.55   $1,215.60