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 $208.95   12.454%   $234.9726   $234.97   $234.95   $235.00  
  Purchase #2 $16.91   6.229%   $17.9633   $17.96   $17.95   $18.00  
  Purchase #3 $82.90   5.383%   $87.3625   $87.36   $87.35   $87.40  
  Purchase #4 $245.83   9.813%   $269.9533   $269.95   $269.95   $270.00  
  Purchase #5 $237.35   11.292%   $264.1516   $264.15   $264.15   $264.20  
  Purchase #6 $73.95   4.720%   $77.4404   $77.44   $77.45   $77.40  
  Purchase #7 $95.47   6.454%   $101.6316   $101.63   $101.65   $101.60  
  7 purchase totals = $961.36       $1,053.4753   $1,053.46   $1,053.45   $1,053.60