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 $154.25   12.353%   $173.3045   $173.30   $173.30   $173.30  
  Purchase #2 $145.46   8.624%   $158.0045   $158.00   $158.00   $158.00  
  Purchase #3 $219.50   3.416%   $226.9981   $227.00   $227.00   $227.00  
  Purchase #4 $94.32   3.856%   $97.957   $97.96   $97.95   $98.00  
  Purchase #5 $167.44   10.331%   $184.7382   $184.74   $184.75   $184.70  
  Purchase #6 $238.87   5.658%   $252.3853   $252.39   $252.40   $252.40  
  Purchase #7 $238.64   6.735%   $254.7124   $254.71   $254.70   $254.70  
  7 purchase totals = $1,258.48       $1,348.1000   $1,348.10   $1,348.10   $1,348.10