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 $202.98   6.636%   $216.4498   $216.45   $216.45   $216.40  
  Purchase #2 $215.51   9.114%   $235.1516   $235.15   $235.15   $235.20  
  Purchase #3 $225.43   10.421%   $248.9221   $248.92   $248.90   $248.90  
  Purchase #4 $15.46   12.862%   $17.4485   $17.45   $17.45   $17.40  
  Purchase #5 $22.56   8.629%   $24.5067   $24.51   $24.50   $24.50  
  Purchase #6 $214.94   10.341%   $237.1669   $237.17   $237.15   $237.20  
  Purchase #7 $215.30   13.865%   $245.1513   $245.15   $245.15   $245.20  
  7 purchase totals = $1,112.18       $1,224.7969   $1,224.80   $1,224.75   $1,224.80