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 $69.58   7.792%   $75.0017   $75.00   $75.00   $75.00  
  Purchase #2 $201.30   4.837%   $211.0369   $211.04   $211.05   $211.00  
  Purchase #3 $160.94   9.261%   $175.8447   $175.84   $175.85   $175.80  
  Purchase #4 $132.33   8.493%   $143.5688   $143.57   $143.55   $143.60  
  Purchase #5 $213.88   3.462%   $221.2845   $221.28   $221.30   $221.30  
  Purchase #6 $173.35   4.506%   $181.1612   $181.16   $181.15   $181.20  
  Purchase #7 $192.76   3.227%   $198.9804   $198.98   $199.00   $199.00  
  7 purchase totals = $1,144.14       $1,206.8782   $1,206.87   $1,206.90   $1,206.90