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 $224.66   10.756%   $248.8244   $248.82   $248.80   $248.80  
  Purchase #2 $106.68   13.336%   $120.9068   $120.91   $120.90   $120.90  
  Purchase #3 $220.93   6.784%   $235.9179   $235.92   $235.90   $235.90  
  Purchase #4 $24.28   7.459%   $26.091   $26.09   $26.10   $26.10  
  Purchase #5 $186.31   11.321%   $207.4022   $207.40   $207.40   $207.40  
  Purchase #6 $220.35   5.604%   $232.6984   $232.70   $232.70   $232.70  
  Purchase #7 $209.89   9.313%   $229.4371   $229.44   $229.45   $229.40  
  7 purchase totals = $1,193.10       $1,301.2778   $1,301.28   $1,301.25   $1,301.20