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 $62.30   9.473%   $68.2017   $68.20   $68.20   $68.20  
  Purchase #2 $231.86   8.475%   $251.5101   $251.51   $251.50   $251.50  
  Purchase #3 $75.96   5.757%   $80.333   $80.33   $80.35   $80.30  
  Purchase #4 $146.62   5.792%   $155.1122   $155.11   $155.10   $155.10  
  Purchase #5 $235.44   7.333%   $252.7048   $252.70   $252.70   $252.70  
  Purchase #6 $164.52   13.407%   $186.5772   $186.58   $186.60   $186.60  
  Purchase #7 $10.96   7.670%   $11.8006   $11.80   $11.80   $11.80  
  7 purchase totals = $927.66       $1,006.2396   $1,006.23   $1,006.25   $1,006.20