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 $86.55   8.770%   $94.1404   $94.14   $94.15   $94.10  
  Purchase #2 $195.33   4.431%   $203.9851   $203.99   $204.00   $204.00  
  Purchase #3 $65.83   8.151%   $71.1958   $71.20   $71.20   $71.20  
  Purchase #4 $117.99   8.127%   $127.579   $127.58   $127.60   $127.60  
  Purchase #5 $144.40   9.540%   $158.1758   $158.18   $158.20   $158.20  
  Purchase #6 $212.58   3.334%   $219.6674   $219.67   $219.65   $219.70  
  Purchase #7 $57.57   10.639%   $63.6949   $63.69   $63.70   $63.70  
  7 purchase totals = $880.25       $938.4384   $938.45   $938.50   $938.50