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 $84.84   9.751%   $93.1127   $93.11   $93.10   $93.10  
  Purchase #2 $173.46   6.782%   $185.2241   $185.22   $185.20   $185.20  
  Purchase #3 $109.59   6.116%   $116.2925   $116.29   $116.30   $116.30  
  Purchase #4 $227.93   6.552%   $242.864   $242.86   $242.85   $242.90  
  Purchase #5 $221.36   5.707%   $233.993   $233.99   $234.00   $234.00  
  Purchase #6 $191.61   6.416%   $203.9037   $203.90   $203.90   $203.90  
  Purchase #7 $93.41   8.594%   $101.4377   $101.44   $101.45   $101.40  
  7 purchase totals = $1,102.20       $1,176.8277   $1,176.81   $1,176.80   $1,176.80