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 $182.79   12.578%   $205.7813   $205.78   $205.80   $205.80  
  Purchase #2 $77.42   6.813%   $82.6946   $82.69   $82.70   $82.70  
  Purchase #3 $122.85   5.126%   $129.1473   $129.15   $129.15   $129.10  
  Purchase #4 $37.68   8.814%   $41.0011   $41.00   $41.00   $41.00  
  Purchase #5 $215.68   11.837%   $241.21   $241.21   $241.20   $241.20  
  Purchase #6 $105.88   13.347%   $120.0118   $120.01   $120.00   $120.00  
  Purchase #7 $170.45   9.827%   $187.2001   $187.20   $187.20   $187.20  
  7 purchase totals = $912.75       $1,007.0462   $1,007.04   $1,007.05   $1,007.00