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 $27.41   7.441%   $29.4496   $29.45   $29.45   $29.40  
  Purchase #2 $142.97   9.505%   $156.5593   $156.56   $156.55   $156.60  
  Purchase #3 $56.86   5.785%   $60.1494   $60.15   $60.15   $60.10  
  Purchase #4 $114.49   10.781%   $126.8332   $126.83   $126.85   $126.80  
  Purchase #5 $227.26   10.713%   $251.6064   $251.61   $251.60   $251.60  
  Purchase #6 $150.26   8.535%   $163.0847   $163.08   $163.10   $163.10  
  Purchase #7 $145.62   10.837%   $161.4008   $161.40   $161.40   $161.40  
  7 purchase totals = $864.87       $949.0834   $949.08   $949.10   $949.00