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 $65.69   7.267%   $70.4637   $70.46   $70.45   $70.50  
  Purchase #2 $63.89   6.805%   $68.2377   $68.24   $68.25   $68.20  
  Purchase #3 $204.64   4.528%   $213.9061   $213.91   $213.90   $213.90  
  Purchase #4 $127.90   13.806%   $145.5579   $145.56   $145.55   $145.60  
  Purchase #5 $34.55   10.299%   $38.1083   $38.11   $38.10   $38.10  
  Purchase #6 $247.72   8.163%   $267.9414   $267.94   $267.95   $267.90  
  Purchase #7 $195.64   7.454%   $210.223   $210.22   $210.20   $210.20  
  7 purchase totals = $940.03       $1,014.4381   $1,014.44   $1,014.40   $1,014.40