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 $235.49   11.694%   $263.0282   $263.03   $263.05   $263.00  
  Purchase #2 $22.79   12.451%   $25.6276   $25.63   $25.65   $25.60  
  Purchase #3 $39.67   3.608%   $41.1013   $41.10   $41.10   $41.10  
  Purchase #4 $42.87   9.121%   $46.7802   $46.78   $46.80   $46.80  
  Purchase #5 $215.61   4.645%   $225.6251   $225.63   $225.65   $225.60  
  Purchase #6 $222.74   7.832%   $240.185   $240.19   $240.20   $240.20  
  Purchase #7 $232.79   13.332%   $263.8256   $263.83   $263.85   $263.80  
  7 purchase totals = $1,011.96       $1,106.1730   $1,106.19   $1,106.30   $1,106.10