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 $86.82   6.771%   $92.6986   $92.70   $92.70   $92.70  
  Purchase #2 $203.46   7.648%   $219.0206   $219.02   $219.00   $219.00  
  Purchase #3 $134.92   9.389%   $147.5876   $147.59   $147.60   $147.60  
  Purchase #4 $71.84   5.114%   $75.5139   $75.51   $75.50   $75.50  
  Purchase #5 $62.31   8.696%   $67.7285   $67.73   $67.75   $67.70  
  Purchase #6 $240.85   9.509%   $263.7524   $263.75   $263.75   $263.80  
  Purchase #7 $185.26   9.194%   $202.2928   $202.29   $202.30   $202.30  
  7 purchase totals = $985.46       $1,068.5944   $1,068.59   $1,068.60   $1,068.60