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 $76.70   8.163%   $82.961   $82.96   $82.95   $83.00  
  Purchase #2 $246.51   5.337%   $259.6662   $259.67   $259.65   $259.70  
  Purchase #3 $165.77   8.316%   $179.5554   $179.56   $179.55   $179.60  
  Purchase #4 $232.59   8.239%   $251.7531   $251.75   $251.75   $251.80  
  Purchase #5 $45.55   4.840%   $47.7546   $47.75   $47.75   $47.80  
  Purchase #6 $233.68   7.400%   $250.9723   $250.97   $250.95   $251.00  
  Purchase #7 $217.62   9.739%   $238.814   $238.81   $238.80   $238.80  
  7 purchase totals = $1,218.42       $1,311.4766   $1,311.47   $1,311.40   $1,311.70