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 $206.68   13.282%   $234.1312   $234.13   $234.15   $234.10  
  Purchase #2 $42.72   9.343%   $46.7113   $46.71   $46.70   $46.70  
  Purchase #3 $216.37   3.188%   $223.2679   $223.27   $223.25   $223.30  
  Purchase #4 $117.91   6.394%   $125.4492   $125.45   $125.45   $125.40  
  Purchase #5 $212.90   8.745%   $231.5181   $231.52   $231.50   $231.50  
  Purchase #6 $220.52   5.373%   $232.3685   $232.37   $232.35   $232.40  
  Purchase #7 $66.90   9.747%   $73.4207   $73.42   $73.40   $73.40  
  7 purchase totals = $1,084.00       $1,166.8669   $1,166.87   $1,166.80   $1,166.80