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 $241.83   11.512%   $269.6695   $269.67   $269.65   $269.70  
  Purchase #2 $235.71   4.329%   $245.9139   $245.91   $245.90   $245.90  
  Purchase #3 $153.40   4.394%   $160.1404   $160.14   $160.15   $160.10  
  Purchase #4 $139.35   11.169%   $154.914   $154.91   $154.90   $154.90  
  Purchase #5 $231.82   10.215%   $255.5004   $255.50   $255.50   $255.50  
  Purchase #6 $25.42   10.806%   $28.1669   $28.17   $28.15   $28.20  
  Purchase #7 $189.86   7.280%   $203.6818   $203.68   $203.70   $203.70  
  7 purchase totals = $1,217.39       $1,317.9869   $1,317.98   $1,317.95   $1,318.00