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 $85.70   11.266%   $95.355   $95.36   $95.35   $95.40  
  Purchase #2 $168.61   6.127%   $178.9407   $178.94   $178.95   $178.90  
  Purchase #3 $239.55   4.777%   $250.9933   $250.99   $251.00   $251.00  
  Purchase #4 $236.30   9.407%   $258.5287   $258.53   $258.55   $258.50  
  Purchase #5 $41.91   8.629%   $45.5264   $45.53   $45.55   $45.50  
  Purchase #6 $179.95   8.271%   $194.8337   $194.83   $194.85   $194.80  
  Purchase #7 $146.74   6.727%   $156.6112   $156.61   $156.60   $156.60  
  7 purchase totals = $1,098.76       $1,180.7890   $1,180.79   $1,180.85   $1,180.70