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 $136.77   7.417%   $146.9142   $146.91   $146.90   $146.90  
  Purchase #2 $64.84   6.399%   $68.9891   $68.99   $69.00   $69.00  
  Purchase #3 $143.51   6.704%   $153.1309   $153.13   $153.15   $153.10  
  Purchase #4 $137.81   13.645%   $156.6142   $156.61   $156.60   $156.60  
  Purchase #5 $220.27   4.835%   $230.9201   $230.92   $230.90   $230.90  
  Purchase #6 $136.85   3.155%   $141.1676   $141.17   $141.15   $141.20  
  Purchase #7 $110.32   5.647%   $116.5498   $116.55   $116.55   $116.50  
  7 purchase totals = $950.37       $1,014.2859   $1,014.28   $1,014.25   $1,014.20