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 $52.62   12.270%   $59.0765   $59.08   $59.10   $59.10  
  Purchase #2 $153.81   9.629%   $168.6204   $168.62   $168.60   $168.60  
  Purchase #3 $233.28   11.357%   $259.7736   $259.77   $259.75   $259.80  
  Purchase #4 $228.72   3.368%   $236.4233   $236.42   $236.40   $236.40  
  Purchase #5 $62.86   5.716%   $66.4531   $66.45   $66.45   $66.50  
  Purchase #6 $167.39   13.159%   $189.4169   $189.42   $189.40   $189.40  
  Purchase #7 $213.41   3.830%   $221.5836   $221.58   $221.60   $221.60  
  7 purchase totals = $1,112.09       $1,201.3474   $1,201.34   $1,201.30   $1,201.40