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 $94.58   8.439%   $102.5616   $102.56   $102.55   $102.60  
  Purchase #2 $34.67   11.231%   $38.5638   $38.56   $38.55   $38.60  
  Purchase #3 $144.84   6.269%   $153.92   $153.92   $153.90   $153.90  
  Purchase #4 $248.36   3.611%   $257.3283   $257.33   $257.35   $257.30  
  Purchase #5 $180.60   7.800%   $194.6868   $194.69   $194.70   $194.70  
  Purchase #6 $211.67   5.472%   $223.2526   $223.25   $223.25   $223.30  
  Purchase #7 $43.53   10.569%   $48.1307   $48.13   $48.15   $48.10  
  7 purchase totals = $958.25       $1,018.4438   $1,018.44   $1,018.45   $1,018.50