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 $165.71   5.163%   $174.2656   $174.27   $174.25   $174.30  
  Purchase #2 $58.74   3.692%   $60.9087   $60.91   $60.90   $60.90  
  Purchase #3 $73.52   9.453%   $80.4698   $80.47   $80.45   $80.50  
  Purchase #4 $187.67   8.188%   $203.0364   $203.04   $203.05   $203.00  
  Purchase #5 $158.76   3.361%   $164.0959   $164.10   $164.10   $164.10  
  Purchase #6 $78.39   11.670%   $87.5381   $87.54   $87.55   $87.50  
  Purchase #7 $40.37   8.126%   $43.6505   $43.65   $43.65   $43.70  
  7 purchase totals = $763.16       $813.9650   $813.98   $813.95   $814.00