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 $62.58   8.666%   $68.0032   $68.00   $68.00   $68.00  
  Purchase #2 $165.93   8.744%   $180.4389   $180.44   $180.45   $180.40  
  Purchase #3 $97.49   12.616%   $109.7893   $109.79   $109.80   $109.80  
  Purchase #4 $247.98   11.489%   $276.4704   $276.47   $276.45   $276.50  
  Purchase #5 $173.49   10.187%   $191.1634   $191.16   $191.15   $191.20  
  Purchase #6 $162.69   10.335%   $179.504   $179.50   $179.50   $179.50  
  Purchase #7 $182.80   8.854%   $198.9851   $198.99   $199.00   $199.00  
  7 purchase totals = $1,092.96       $1,204.3543   $1,204.35   $1,204.35   $1,204.40