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 $53.34   13.722%   $60.6593   $60.66   $60.65   $60.70  
  Purchase #2 $88.79   3.598%   $91.9847   $91.98   $92.00   $92.00  
  Purchase #3 $182.68   3.238%   $188.5952   $188.60   $188.60   $188.60  
  Purchase #4 $77.72   4.671%   $81.3503   $81.35   $81.35   $81.40  
  Purchase #5 $208.40   12.581%   $234.6188   $234.62   $234.60   $234.60  
  Purchase #6 $236.83   11.701%   $264.5415   $264.54   $264.55   $264.50  
  Purchase #7 $220.84   6.862%   $235.994   $235.99   $236.00   $236.00  
  7 purchase totals = $1,068.60       $1,157.7438   $1,157.74   $1,157.75   $1,157.80