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 $248.34   11.268%   $276.323   $276.32   $276.30   $276.30  
  Purchase #2 $149.72   10.437%   $165.3463   $165.35   $165.35   $165.30  
  Purchase #3 $87.97   11.649%   $98.2176   $98.22   $98.20   $98.20  
  Purchase #4 $196.28   7.437%   $210.8773   $210.88   $210.90   $210.90  
  Purchase #5 $14.59   13.613%   $16.5761   $16.58   $16.60   $16.60  
  Purchase #6 $95.71   12.226%   $107.4115   $107.41   $107.40   $107.40  
  Purchase #7 $83.37   5.631%   $88.0646   $88.06   $88.05   $88.10  
  7 purchase totals = $875.98       $962.8164   $962.82   $962.80   $962.80