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 $232.98   8.273%   $252.2544   $252.25   $252.25   $252.30  
  Purchase #2 $56.26   13.767%   $64.0053   $64.01   $64.00   $64.00  
  Purchase #3 $47.48   3.775%   $49.2724   $49.27   $49.25   $49.30  
  Purchase #4 $88.35   7.439%   $94.9224   $94.92   $94.90   $94.90  
  Purchase #5 $187.51   8.340%   $203.1483   $203.15   $203.15   $203.10  
  Purchase #6 $161.79   9.152%   $176.597   $176.60   $176.60   $176.60  
  Purchase #7 $189.81   3.572%   $196.59   $196.59   $196.60   $196.60  
  7 purchase totals = $964.18       $1,036.7898   $1,036.79   $1,036.75   $1,036.80