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 $91.94   5.689%   $97.1705   $97.17   $97.15   $97.20  
  Purchase #2 $237.43   11.607%   $264.9885   $264.99   $265.00   $265.00  
  Purchase #3 $64.44   8.744%   $70.0746   $70.07   $70.05   $70.10  
  Purchase #4 $216.74   6.302%   $230.399   $230.40   $230.40   $230.40  
  Purchase #5 $166.89   10.311%   $184.098   $184.10   $184.10   $184.10  
  Purchase #6 $164.73   13.219%   $186.5057   $186.51   $186.50   $186.50  
  Purchase #7 $209.28   10.407%   $231.0598   $231.06   $231.05   $231.10  
  7 purchase totals = $1,151.45       $1,264.2961   $1,264.30   $1,264.25   $1,264.40