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 $196.51   13.523%   $223.084   $223.08   $223.10   $223.10  
  Purchase #2 $207.69   11.833%   $232.266   $232.27   $232.25   $232.30  
  Purchase #3 $51.46   5.285%   $54.1797   $54.18   $54.20   $54.20  
  Purchase #4 $103.97   12.676%   $117.1492   $117.15   $117.15   $117.10  
  Purchase #5 $245.30   3.559%   $254.0302   $254.03   $254.05   $254.00  
  Purchase #6 $98.43   8.702%   $106.9954   $107.00   $107.00   $107.00  
  Purchase #7 $229.58   9.553%   $251.5118   $251.51   $251.50   $251.50  
  7 purchase totals = $1,132.94       $1,239.2163   $1,239.22   $1,239.25   $1,239.20