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 $92.29   4.791%   $96.7116   $96.71   $96.70   $96.70  
  Purchase #2 $192.85   7.571%   $207.4507   $207.45   $207.45   $207.50  
  Purchase #3 $166.53   4.475%   $173.9822   $173.98   $174.00   $174.00  
  Purchase #4 $75.40   7.742%   $81.2375   $81.24   $81.25   $81.20  
  Purchase #5 $150.64   11.540%   $168.0239   $168.02   $168.00   $168.00  
  Purchase #6 $70.64   12.240%   $79.2863   $79.29   $79.30   $79.30  
  Purchase #7 $91.43   5.703%   $96.6443   $96.64   $96.65   $96.60  
  7 purchase totals = $839.78       $903.3365   $903.33   $903.35   $903.30