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 $61.51   7.650%   $66.2155   $66.22   $66.20   $66.20  
  Purchase #2 $23.78   11.534%   $26.5228   $26.52   $26.50   $26.50  
  Purchase #3 $157.67   4.518%   $164.7935   $164.79   $164.80   $164.80  
  Purchase #4 $206.42   8.256%   $223.462   $223.46   $223.45   $223.50  
  Purchase #5 $216.27   4.623%   $226.2682   $226.27   $226.25   $226.30  
  Purchase #6 $246.87   10.856%   $273.6702   $273.67   $273.65   $273.70  
  Purchase #7 $163.61   12.671%   $184.341   $184.34   $184.35   $184.30  
  7 purchase totals = $1,076.13       $1,165.2732   $1,165.27   $1,165.20   $1,165.30