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 $61.96   6.465%   $65.9657   $65.97   $65.95   $66.00  
  Purchase #2 $243.38   9.501%   $266.5035   $266.50   $266.50   $266.50  
  Purchase #3 $203.81   7.108%   $218.2968   $218.30   $218.30   $218.30  
  Purchase #4 $151.85   11.355%   $169.0926   $169.09   $169.10   $169.10  
  Purchase #5 $91.80   12.508%   $103.2823   $103.28   $103.30   $103.30  
  Purchase #6 $233.79   7.763%   $251.9391   $251.94   $251.95   $251.90  
  Purchase #7 $30.86   10.793%   $34.1907   $34.19   $34.20   $34.20  
  7 purchase totals = $1,017.45       $1,109.2707   $1,109.27   $1,109.30   $1,109.30