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 $212.66   10.647%   $235.3019   $235.30   $235.30   $235.30  
  Purchase #2 $219.71   11.851%   $245.7478   $245.75   $245.75   $245.70  
  Purchase #3 $204.28   11.540%   $227.8539   $227.85   $227.85   $227.90  
  Purchase #4 $211.26   4.629%   $221.0392   $221.04   $221.05   $221.00  
  Purchase #5 $19.86   12.763%   $22.3947   $22.39   $22.40   $22.40  
  Purchase #6 $219.95   4.584%   $230.0325   $230.03   $230.05   $230.00  
  Purchase #7 $134.84   4.471%   $140.8687   $140.87   $140.85   $140.90  
  7 purchase totals = $1,222.56       $1,323.2387   $1,323.23   $1,323.25   $1,323.20