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 $204.71   13.660%   $232.6734   $232.67   $232.65   $232.70  
  Purchase #2 $43.66   10.658%   $48.3133   $48.31   $48.30   $48.30  
  Purchase #3 $223.50   12.855%   $252.2309   $252.23   $252.25   $252.20  
  Purchase #4 $58.64   13.832%   $66.7511   $66.75   $66.75   $66.80  
  Purchase #5 $220.26   4.359%   $229.8611   $229.86   $229.85   $229.90  
  Purchase #6 $36.91   9.583%   $40.4471   $40.45   $40.45   $40.40  
  Purchase #7 $148.58   8.853%   $161.7338   $161.73   $161.75   $161.70  
  7 purchase totals = $936.26       $1,032.0107   $1,032.00   $1,032.00   $1,032.00