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 $207.55   7.755%   $223.6455   $223.65   $223.65   $223.60  
  Purchase #2 $119.97   11.244%   $133.4594   $133.46   $133.45   $133.50  
  Purchase #3 $101.87   4.446%   $106.3991   $106.40   $106.40   $106.40  
  Purchase #4 $230.71   4.377%   $240.8082   $240.81   $240.80   $240.80  
  Purchase #5 $109.40   4.874%   $114.7322   $114.73   $114.75   $114.70  
  Purchase #6 $138.27   11.230%   $153.7977   $153.80   $153.80   $153.80  
  Purchase #7 $21.42   4.110%   $22.3004   $22.30   $22.30   $22.30  
  7 purchase totals = $929.19       $995.1425   $995.15   $995.15   $995.10