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 $198.52   8.559%   $215.5113   $215.51   $215.50   $215.50  
  Purchase #2 $223.87   10.740%   $247.9136   $247.91   $247.90   $247.90  
  Purchase #3 $211.88   9.700%   $232.4324   $232.43   $232.45   $232.40  
  Purchase #4 $195.63   6.787%   $208.9074   $208.91   $208.90   $208.90  
  Purchase #5 $33.95   3.505%   $35.1399   $35.14   $35.15   $35.10  
  Purchase #6 $106.98   6.647%   $114.091   $114.09   $114.10   $114.10  
  Purchase #7 $162.98   5.689%   $172.2519   $172.25   $172.25   $172.30  
  7 purchase totals = $1,133.81       $1,226.2475   $1,226.24   $1,226.25   $1,226.20