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 $183.67   4.471%   $191.8819   $191.88   $191.90   $191.90  
  Purchase #2 $245.70   6.797%   $262.4002   $262.40   $262.40   $262.40  
  Purchase #3 $197.98   10.106%   $217.9879   $217.99   $218.00   $218.00  
  Purchase #4 $60.55   7.418%   $65.0416   $65.04   $65.05   $65.00  
  Purchase #5 $219.72   9.367%   $240.3012   $240.30   $240.30   $240.30  
  Purchase #6 $246.33   9.568%   $269.8989   $269.90   $269.90   $269.90  
  Purchase #7 $13.47   11.318%   $14.9945   $14.99   $15.00   $15.00  
  7 purchase totals = $1,167.42       $1,262.5062   $1,262.50   $1,262.55   $1,262.50