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 $63.78   8.118%   $68.9577   $68.96   $68.95   $69.00  
  Purchase #2 $184.91   5.657%   $195.3704   $195.37   $195.35   $195.40  
  Purchase #3 $88.93   13.766%   $101.1721   $101.17   $101.15   $101.20  
  Purchase #4 $133.43   13.476%   $151.411   $151.41   $151.40   $151.40  
  Purchase #5 $209.95   3.285%   $216.8469   $216.85   $216.85   $216.80  
  Purchase #6 $100.25   6.651%   $106.9176   $106.92   $106.90   $106.90  
  Purchase #7 $228.66   13.476%   $259.4742   $259.47   $259.45   $259.50  
  7 purchase totals = $1,009.91       $1,100.1499   $1,100.15   $1,100.05   $1,100.20