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 $176.52   13.493%   $200.3378   $200.34   $200.35   $200.30  
  Purchase #2 $60.73   4.494%   $63.4592   $63.46   $63.45   $63.50  
  Purchase #3 $150.88   6.805%   $161.1474   $161.15   $161.15   $161.10  
  Purchase #4 $33.75   4.587%   $35.2981   $35.30   $35.30   $35.30  
  Purchase #5 $235.62   12.855%   $265.909   $265.91   $265.90   $265.90  
  Purchase #6 $208.30   9.627%   $228.353   $228.35   $228.35   $228.40  
  Purchase #7 $160.71   9.332%   $175.7075   $175.71   $175.70   $175.70  
  7 purchase totals = $1,026.51       $1,130.2120   $1,130.22   $1,130.20   $1,130.20