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 $212.76   11.145%   $236.4721   $236.47   $236.45   $236.50  
  Purchase #2 $134.79   3.124%   $139.0008   $139.00   $139.00   $139.00  
  Purchase #3 $65.36   4.203%   $68.1071   $68.11   $68.10   $68.10  
  Purchase #4 $77.58   7.405%   $83.3248   $83.32   $83.30   $83.30  
  Purchase #5 $136.31   13.223%   $154.3343   $154.33   $154.35   $154.30  
  Purchase #6 $227.53   9.684%   $249.564   $249.56   $249.55   $249.60  
  Purchase #7 $142.81   6.592%   $152.224   $152.22   $152.20   $152.20  
  7 purchase totals = $997.14       $1,083.0271   $1,083.01   $1,082.95   $1,083.00