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 $70.26   8.179%   $76.0066   $76.01   $76.00   $76.00  
  Purchase #2 $86.47   9.171%   $94.4002   $94.40   $94.40   $94.40  
  Purchase #3 $120.52   8.243%   $130.4545   $130.45   $130.45   $130.50  
  Purchase #4 $137.84   3.311%   $142.4039   $142.40   $142.40   $142.40  
  Purchase #5 $159.53   9.871%   $175.2772   $175.28   $175.30   $175.30  
  Purchase #6 $6.44   4.436%   $6.7257   $6.73   $6.75   $6.70  
  Purchase #7 $154.33   3.774%   $160.1544   $160.15   $160.15   $160.20  
  7 purchase totals = $735.39       $785.4225   $785.42   $785.45   $785.50