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 $29.35   11.783%   $32.8083   $32.81   $32.80   $32.80  
  Purchase #2 $109.99   9.410%   $120.3401   $120.34   $120.35   $120.30  
  Purchase #3 $215.96   5.506%   $227.8508   $227.85   $227.85   $227.90  
  Purchase #4 $158.51   6.402%   $168.6578   $168.66   $168.65   $168.70  
  Purchase #5 $191.69   6.377%   $203.9141   $203.91   $203.90   $203.90  
  Purchase #6 $133.95   5.229%   $140.9542   $140.95   $140.95   $141.00  
  Purchase #7 $117.36   10.743%   $129.968   $129.97   $129.95   $130.00  
  7 purchase totals = $956.81       $1,024.4933   $1,024.49   $1,024.45   $1,024.60