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 $25.39   8.542%   $27.5588   $27.56   $27.55   $27.60  
  Purchase #2 $118.28   7.845%   $127.5591   $127.56   $127.55   $127.60  
  Purchase #3 $208.81   13.479%   $236.9555   $236.96   $236.95   $237.00  
  Purchase #4 $187.85   5.560%   $198.2945   $198.29   $198.30   $198.30  
  Purchase #5 $177.53   11.492%   $197.9317   $197.93   $197.95   $197.90  
  Purchase #6 $111.45   11.574%   $124.3492   $124.35   $124.35   $124.30  
  Purchase #7 $123.37   5.363%   $129.9863   $129.99   $130.00   $130.00  
  7 purchase totals = $952.68       $1,042.6351   $1,042.64   $1,042.65   $1,042.70