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 $246.26   9.626%   $269.965   $269.97   $269.95   $270.00  
  Purchase #2 $235.87   3.335%   $243.7363   $243.74   $243.75   $243.70  
  Purchase #3 $39.93   3.333%   $41.2609   $41.26   $41.25   $41.30  
  Purchase #4 $160.51   6.239%   $170.5242   $170.52   $170.50   $170.50  
  Purchase #5 $191.86   11.493%   $213.9105   $213.91   $213.90   $213.90  
  Purchase #6 $229.81   11.382%   $255.967   $255.97   $255.95   $256.00  
  Purchase #7 $132.63   10.838%   $147.0044   $147.00   $147.00   $147.00  
  7 purchase totals = $1,236.87       $1,342.3683   $1,342.37   $1,342.30   $1,342.40