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 $156.25   12.638%   $175.9969   $176.00   $176.00   $176.00  
  Purchase #2 $190.93   8.705%   $207.5505   $207.55   $207.55   $207.60  
  Purchase #3 $29.45   13.333%   $33.3766   $33.38   $33.40   $33.40  
  Purchase #4 $191.52   11.732%   $213.9891   $213.99   $214.00   $214.00  
  Purchase #5 $112.62   13.421%   $127.7347   $127.73   $127.75   $127.70  
  Purchase #6 $155.40   11.382%   $173.0876   $173.09   $173.10   $173.10  
  Purchase #7 $87.54   8.443%   $94.931   $94.93   $94.95   $94.90  
  7 purchase totals = $923.71       $1,026.6664   $1,026.67   $1,026.75   $1,026.70