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 $59.83   3.519%   $61.9354   $61.94   $61.95   $61.90  
  Purchase #2 $118.47   6.205%   $125.8211   $125.82   $125.80   $125.80  
  Purchase #3 $114.79   9.712%   $125.9384   $125.94   $125.95   $125.90  
  Purchase #4 $209.57   8.253%   $226.8658   $226.87   $226.85   $226.90  
  Purchase #5 $37.98   12.428%   $42.7002   $42.70   $42.70   $42.70  
  Purchase #6 $249.55   6.311%   $265.2991   $265.30   $265.30   $265.30  
  Purchase #7 $49.36   3.190%   $50.9346   $50.93   $50.95   $50.90  
  7 purchase totals = $839.55       $899.4946   $899.50   $899.50   $899.40