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 $5.48   6.584%   $5.8408   $5.84   $5.85   $5.80  
  Purchase #2 $244.71   3.661%   $253.6688   $253.67   $253.65   $253.70  
  Purchase #3 $114.63   13.576%   $130.1922   $130.19   $130.20   $130.20  
  Purchase #4 $23.51   12.860%   $26.5334   $26.53   $26.55   $26.50  
  Purchase #5 $168.88   8.659%   $183.5033   $183.50   $183.50   $183.50  
  Purchase #6 $244.65   11.623%   $273.0857   $273.09   $273.10   $273.10  
  Purchase #7 $166.91   12.224%   $187.3131   $187.31   $187.30   $187.30  
  7 purchase totals = $968.77       $1,060.1373   $1,060.13   $1,060.15   $1,060.10