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 $154.76   12.816%   $174.594   $174.59   $174.60   $174.60  
  Purchase #2 $62.69   6.696%   $66.8877   $66.89   $66.90   $66.90  
  Purchase #3 $197.53   8.325%   $213.9744   $213.97   $213.95   $214.00  
  Purchase #4 $167.45   13.708%   $190.404   $190.40   $190.40   $190.40  
  Purchase #5 $178.45   7.826%   $192.4155   $192.42   $192.40   $192.40  
  Purchase #6 $132.30   11.617%   $147.6693   $147.67   $147.65   $147.70  
  Purchase #7 $97.91   4.567%   $102.3815   $102.38   $102.40   $102.40  
  7 purchase totals = $991.09       $1,088.3264   $1,088.32   $1,088.30   $1,088.40