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 $124.69   7.651%   $134.23   $134.23   $134.25   $134.20  
  Purchase #2 $170.53   3.769%   $176.9573   $176.96   $176.95   $177.00  
  Purchase #3 $105.96   7.782%   $114.2058   $114.21   $114.20   $114.20  
  Purchase #4 $23.26   3.144%   $23.9913   $23.99   $24.00   $24.00  
  Purchase #5 $61.34   6.654%   $65.4216   $65.42   $65.40   $65.40  
  Purchase #6 $23.29   12.450%   $26.1896   $26.19   $26.20   $26.20  
  Purchase #7 $65.42   13.469%   $74.2314   $74.23   $74.25   $74.20  
  7 purchase totals = $574.49       $615.2270   $615.23   $615.25   $615.20