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 $234.29   5.386%   $246.9089   $246.91   $246.90   $246.90  
  Purchase #2 $52.94   6.585%   $56.4261   $56.43   $56.45   $56.40  
  Purchase #3 $74.42   6.521%   $79.2729   $79.27   $79.25   $79.30  
  Purchase #4 $64.85   12.315%   $72.8363   $72.84   $72.85   $72.80  
  Purchase #5 $170.28   5.724%   $180.0268   $180.03   $180.05   $180.00  
  Purchase #6 $122.33   10.561%   $135.2493   $135.25   $135.25   $135.20  
  Purchase #7 $249.54   13.871%   $284.1537   $284.15   $284.15   $284.20  
  7 purchase totals = $968.65       $1,054.8740   $1,054.88   $1,054.90   $1,054.80