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 $87.92   8.821%   $95.6754   $95.68   $95.70   $95.70  
  Purchase #2 $80.73   6.287%   $85.8055   $85.81   $85.80   $85.80  
  Purchase #3 $165.49   13.469%   $187.7798   $187.78   $187.80   $187.80  
  Purchase #4 $84.74   11.334%   $94.3444   $94.34   $94.35   $94.30  
  Purchase #5 $180.29   4.357%   $188.1452   $188.15   $188.15   $188.10  
  Purchase #6 $73.43   12.464%   $82.5823   $82.58   $82.60   $82.60  
  Purchase #7 $38.60   6.487%   $41.104   $41.10   $41.10   $41.10  
  7 purchase totals = $711.20       $775.4366   $775.44   $775.50   $775.40