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 $160.34   5.408%   $169.0112   $169.01   $169.00   $169.00  
  Purchase #2 $51.32   5.122%   $53.9486   $53.95   $53.95   $53.90  
  Purchase #3 $115.95   5.786%   $122.6589   $122.66   $122.65   $122.70  
  Purchase #4 $56.98   6.515%   $60.6922   $60.69   $60.70   $60.70  
  Purchase #5 $247.80   6.739%   $264.4992   $264.50   $264.50   $264.50  
  Purchase #6 $245.74   12.493%   $276.4403   $276.44   $276.45   $276.40  
  Purchase #7 $175.92   13.800%   $200.197   $200.20   $200.20   $200.20  
  7 purchase totals = $1,054.05       $1,147.4474   $1,147.45   $1,147.45   $1,147.40