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 $85.32   12.841%   $96.2759   $96.28   $96.30   $96.30  
  Purchase #2 $150.40   4.436%   $157.0717   $157.07   $157.05   $157.10  
  Purchase #3 $60.29   4.164%   $62.8005   $62.80   $62.80   $62.80  
  Purchase #4 $81.99   4.821%   $85.9427   $85.94   $85.95   $85.90  
  Purchase #5 $89.65   6.779%   $95.7274   $95.73   $95.75   $95.70  
  Purchase #6 $80.45   7.494%   $86.4789   $86.48   $86.50   $86.50  
  Purchase #7 $223.42   8.589%   $242.6095   $242.61   $242.60   $242.60  
  7 purchase totals = $771.52       $826.9066   $826.91   $826.95   $826.90