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 $56.51   5.551%   $59.6469   $59.65   $59.65   $59.60  
  Purchase #2 $148.82   12.355%   $167.2067   $167.21   $167.20   $167.20  
  Purchase #3 $59.90   6.531%   $63.8121   $63.81   $63.80   $63.80  
  Purchase #4 $220.89   13.361%   $250.4031   $250.40   $250.40   $250.40  
  Purchase #5 $178.53   4.196%   $186.0211   $186.02   $186.00   $186.00  
  Purchase #6 $193.25   10.541%   $213.6205   $213.62   $213.60   $213.60  
  Purchase #7 $83.86   3.622%   $86.8974   $86.90   $86.90   $86.90  
  7 purchase totals = $941.76       $1,027.6078   $1,027.61   $1,027.55   $1,027.50