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 $108.68   8.718%   $118.1547   $118.15   $118.15   $118.20  
  Purchase #2 $203.65   6.403%   $216.6897   $216.69   $216.70   $216.70  
  Purchase #3 $86.90   11.365%   $96.7762   $96.78   $96.80   $96.80  
  Purchase #4 $218.45   8.573%   $237.1777   $237.18   $237.20   $237.20  
  Purchase #5 $54.95   10.318%   $60.6197   $60.62   $60.60   $60.60  
  Purchase #6 $49.48   13.662%   $56.24   $56.24   $56.25   $56.20  
  Purchase #7 $156.28   12.603%   $175.976   $175.98   $176.00   $176.00  
  7 purchase totals = $878.39       $961.6340   $961.64   $961.70   $961.70