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 $246.60   9.241%   $269.3883   $269.39   $269.40   $269.40  
  Purchase #2 $94.74   13.362%   $107.3992   $107.40   $107.40   $107.40  
  Purchase #3 $205.26   5.684%   $216.927   $216.93   $216.95   $216.90  
  Purchase #4 $168.80   12.318%   $189.5928   $189.59   $189.60   $189.60  
  Purchase #5 $66.25   13.872%   $75.4402   $75.44   $75.45   $75.40  
  Purchase #6 $51.49   12.461%   $57.9062   $57.91   $57.90   $57.90  
  Purchase #7 $156.46   4.195%   $163.0235   $163.02   $163.00   $163.00  
  7 purchase totals = $989.60       $1,079.6772   $1,079.68   $1,079.70   $1,079.60