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 $239.58   9.356%   $261.9951   $262.00   $262.00   $262.00  
  Purchase #2 $22.34   9.852%   $24.5409   $24.54   $24.55   $24.50  
  Purchase #3 $83.66   8.426%   $90.7092   $90.71   $90.70   $90.70  
  Purchase #4 $216.30   5.370%   $227.9153   $227.92   $227.90   $227.90  
  Purchase #5 $226.35   13.148%   $256.1105   $256.11   $256.10   $256.10  
  Purchase #6 $183.27   12.112%   $205.4677   $205.47   $205.45   $205.50  
  Purchase #7 $218.96   7.542%   $235.474   $235.47   $235.45   $235.50  
  7 purchase totals = $1,190.46       $1,302.2127   $1,302.22   $1,302.15   $1,302.20