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 $86.98   6.832%   $92.9225   $92.92   $92.90   $92.90  
  Purchase #2 $183.58   5.667%   $193.9835   $193.98   $194.00   $194.00  
  Purchase #3 $173.91   4.533%   $181.7933   $181.79   $181.80   $181.80  
  Purchase #4 $60.89   9.621%   $66.7482   $66.75   $66.75   $66.70  
  Purchase #5 $240.31   7.742%   $258.9148   $258.91   $258.90   $258.90  
  Purchase #6 $38.45   7.603%   $41.3734   $41.37   $41.35   $41.40  
  Purchase #7 $197.27   8.426%   $213.892   $213.89   $213.90   $213.90  
  7 purchase totals = $981.39       $1,049.6277   $1,049.61   $1,049.60   $1,049.60