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 $62.96   10.598%   $69.6325   $69.63   $69.65   $69.60  
  Purchase #2 $54.31   3.683%   $56.3102   $56.31   $56.30   $56.30  
  Purchase #3 $242.37   5.481%   $255.6543   $255.65   $255.65   $255.70  
  Purchase #4 $134.88   5.544%   $142.3577   $142.36   $142.35   $142.40  
  Purchase #5 $29.91   11.652%   $33.3951   $33.40   $33.40   $33.40  
  Purchase #6 $91.29   5.614%   $96.415   $96.42   $96.40   $96.40  
  Purchase #7 $41.25   4.309%   $43.0275   $43.03   $43.05   $43.00  
  7 purchase totals = $656.97       $696.7923   $696.80   $696.80   $696.80