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 $56.67   13.431%   $64.2813   $64.28   $64.30   $64.30  
  Purchase #2 $87.57   8.647%   $95.1422   $95.14   $95.15   $95.10  
  Purchase #3 $208.39   12.215%   $233.8448   $233.84   $233.85   $233.80  
  Purchase #4 $240.91   12.800%   $271.7465   $271.75   $271.75   $271.70  
  Purchase #5 $85.71   13.107%   $96.944   $96.94   $96.95   $96.90  
  Purchase #6 $153.41   9.768%   $168.3951   $168.40   $168.40   $168.40  
  Purchase #7 $34.52   4.255%   $35.9888   $35.99   $36.00   $36.00  
  7 purchase totals = $867.18       $966.3427   $966.34   $966.40   $966.20