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 $64.55   10.759%   $71.4949   $71.49   $71.50   $71.50  
  Purchase #2 $153.91   3.447%   $159.2153   $159.22   $159.20   $159.20  
  Purchase #3 $234.78   7.240%   $251.7781   $251.78   $251.80   $251.80  
  Purchase #4 $71.64   3.287%   $73.9948   $73.99   $74.00   $74.00  
  Purchase #5 $249.28   4.873%   $261.4274   $261.43   $261.45   $261.40  
  Purchase #6 $205.70   6.759%   $219.6033   $219.60   $219.60   $219.60  
  Purchase #7 $40.64   13.740%   $46.2239   $46.22   $46.20   $46.20  
  7 purchase totals = $1,020.50       $1,083.7377   $1,083.73   $1,083.75   $1,083.70