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 $186.55   12.346%   $209.5815   $209.58   $209.60   $209.60  
  Purchase #2 $50.73   11.488%   $56.5579   $56.56   $56.55   $56.60  
  Purchase #3 $155.32   12.522%   $174.7692   $174.77   $174.75   $174.80  
  Purchase #4 $23.28   4.374%   $24.2983   $24.30   $24.30   $24.30  
  Purchase #5 $96.36   10.608%   $106.5819   $106.58   $106.60   $106.60  
  Purchase #6 $189.43   3.594%   $196.2381   $196.24   $196.25   $196.20  
  Purchase #7 $184.44   5.496%   $194.5768   $194.58   $194.60   $194.60  
  7 purchase totals = $886.11       $962.6037   $962.61   $962.65   $962.70