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 $91.92   7.678%   $98.9776   $98.98   $99.00   $99.00  
  Purchase #2 $163.84   9.248%   $178.9919   $178.99   $179.00   $179.00  
  Purchase #3 $192.87   4.355%   $201.2695   $201.27   $201.25   $201.30  
  Purchase #4 $59.58   5.663%   $62.954   $62.95   $62.95   $63.00  
  Purchase #5 $188.49   8.168%   $203.8859   $203.89   $203.90   $203.90  
  Purchase #6 $75.55   5.782%   $79.9183   $79.92   $79.90   $79.90  
  Purchase #7 $178.51   12.748%   $201.2665   $201.27   $201.25   $201.30  
  7 purchase totals = $950.76       $1,027.2637   $1,027.27   $1,027.25   $1,027.40