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 $131.55   9.162%   $143.6026   $143.60   $143.60   $143.60  
  Purchase #2 $200.56   11.365%   $223.3536   $223.35   $223.35   $223.40  
  Purchase #3 $242.25   8.439%   $262.6935   $262.69   $262.70   $262.70  
  Purchase #4 $86.77   8.568%   $94.2045   $94.20   $94.20   $94.20  
  Purchase #5 $213.63   8.538%   $231.8697   $231.87   $231.85   $231.90  
  Purchase #6 $247.97   13.363%   $281.1062   $281.11   $281.10   $281.10  
  Purchase #7 $29.70   6.616%   $31.665   $31.67   $31.65   $31.70  
  7 purchase totals = $1,152.43       $1,268.4951   $1,268.49   $1,268.45   $1,268.60