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 $247.67   11.305%   $275.6691   $275.67   $275.65   $275.70  
  Purchase #2 $238.59   11.184%   $265.2739   $265.27   $265.25   $265.30  
  Purchase #3 $65.44   5.724%   $69.1858   $69.19   $69.20   $69.20  
  Purchase #4 $197.69   5.255%   $208.0786   $208.08   $208.10   $208.10  
  Purchase #5 $41.74   4.590%   $43.6559   $43.66   $43.65   $43.70  
  Purchase #6 $64.79   8.662%   $70.4021   $70.40   $70.40   $70.40  
  Purchase #7 $84.74   11.465%   $94.4554   $94.46   $94.45   $94.50  
  7 purchase totals = $940.66       $1,026.7208   $1,026.73   $1,026.70   $1,026.90