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 $88.92   9.849%   $97.6777   $97.68   $97.70   $97.70  
  Purchase #2 $61.59   7.108%   $65.9678   $65.97   $65.95   $66.00  
  Purchase #3 $76.37   9.728%   $83.7993   $83.80   $83.80   $83.80  
  Purchase #4 $185.44   3.813%   $192.5108   $192.51   $192.50   $192.50  
  Purchase #5 $249.27   6.436%   $265.313   $265.31   $265.30   $265.30  
  Purchase #6 $191.59   3.604%   $198.4949   $198.49   $198.50   $198.50  
  Purchase #7 $119.87   9.629%   $131.4123   $131.41   $131.40   $131.40  
  7 purchase totals = $973.05       $1,035.1758   $1,035.17   $1,035.15   $1,035.20