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 $184.53   11.197%   $205.1918   $205.19   $205.20   $205.20  
  Purchase #2 $214.40   9.270%   $234.2749   $234.27   $234.25   $234.30  
  Purchase #3 $35.36   12.397%   $39.7436   $39.74   $39.75   $39.70  
  Purchase #4 $132.96   11.518%   $148.2743   $148.27   $148.25   $148.30  
  Purchase #5 $213.94   11.843%   $239.2769   $239.28   $239.30   $239.30  
  Purchase #6 $122.83   11.644%   $137.1323   $137.13   $137.15   $137.10  
  Purchase #7 $127.28   12.381%   $143.0385   $143.04   $143.05   $143.00  
  7 purchase totals = $1,031.30       $1,146.9323   $1,146.92   $1,146.95   $1,146.90