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 $231.91   6.437%   $246.838   $246.84   $246.85   $246.80  
  Purchase #2 $211.86   13.626%   $240.728   $240.73   $240.75   $240.70  
  Purchase #3 $91.70   11.397%   $102.151   $102.15   $102.15   $102.20  
  Purchase #4 $160.41   6.668%   $171.1061   $171.11   $171.10   $171.10  
  Purchase #5 $161.90   4.193%   $168.6885   $168.69   $168.70   $168.70  
  Purchase #6 $216.37   13.471%   $245.5172   $245.52   $245.50   $245.50  
  Purchase #7 $250.81   7.522%   $269.6759   $269.68   $269.70   $269.70  
  7 purchase totals = $1,324.96       $1,444.7047   $1,444.72   $1,444.75   $1,444.70