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 $247.98   8.548%   $269.1773   $269.18   $269.20   $269.20  
  Purchase #2 $82.50   5.284%   $86.8593   $86.86   $86.85   $86.90  
  Purchase #3 $40.84   5.194%   $42.9612   $42.96   $42.95   $43.00  
  Purchase #4 $108.57   5.370%   $114.4002   $114.40   $114.40   $114.40  
  Purchase #5 $128.37   8.420%   $139.1788   $139.18   $139.20   $139.20  
  Purchase #6 $134.79   13.675%   $153.2225   $153.22   $153.20   $153.20  
  Purchase #7 $110.67   8.505%   $120.0825   $120.08   $120.10   $120.10  
  7 purchase totals = $853.72       $925.8818   $925.88   $925.90   $926.00