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 $201.35   12.362%   $226.2409   $226.24   $226.25   $226.20  
  Purchase #2 $142.59   4.445%   $148.9281   $148.93   $148.95   $148.90  
  Purchase #3 $129.89   13.707%   $147.694   $147.69   $147.70   $147.70  
  Purchase #4 $114.57   12.460%   $128.8454   $128.85   $128.85   $128.80  
  Purchase #5 $29.56   5.530%   $31.1947   $31.19   $31.20   $31.20  
  Purchase #6 $215.51   10.724%   $238.6213   $238.62   $238.60   $238.60  
  Purchase #7 $118.49   3.645%   $122.809   $122.81   $122.80   $122.80  
  7 purchase totals = $951.96       $1,044.3334   $1,044.33   $1,044.35   $1,044.20