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 $59.72   13.860%   $67.9972   $68.00   $68.00   $68.00  
  Purchase #2 $220.81   7.223%   $236.7591   $236.76   $236.75   $236.80  
  Purchase #3 $199.73   8.232%   $216.1718   $216.17   $216.15   $216.20  
  Purchase #4 $38.96   4.560%   $40.7366   $40.74   $40.75   $40.70  
  Purchase #5 $32.76   4.222%   $34.1431   $34.14   $34.15   $34.10  
  Purchase #6 $75.62   7.270%   $81.1176   $81.12   $81.10   $81.10  
  Purchase #7 $248.60   9.576%   $272.4059   $272.41   $272.40   $272.40  
  7 purchase totals = $876.20       $949.3313   $949.34   $949.30   $949.30