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 $127.96   5.584%   $135.1053   $135.11   $135.10   $135.10  
  Purchase #2 $79.45   5.638%   $83.9294   $83.93   $83.95   $83.90  
  Purchase #3 $53.62   12.441%   $60.2909   $60.29   $60.30   $60.30  
  Purchase #4 $87.86   3.472%   $90.9105   $90.91   $90.90   $90.90  
  Purchase #5 $45.40   10.590%   $50.2079   $50.21   $50.20   $50.20  
  Purchase #6 $7.30   10.768%   $8.0861   $8.09   $8.10   $8.10  
  Purchase #7 $245.94   10.335%   $271.3579   $271.36   $271.35   $271.40  
  7 purchase totals = $647.53       $699.8880   $699.90   $699.90   $699.90