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 $38.90   11.868%   $43.5167   $43.52   $43.50   $43.50  
  Purchase #2 $58.78   12.278%   $65.997   $66.00   $66.00   $66.00  
  Purchase #3 $139.54   13.619%   $158.544   $158.54   $158.55   $158.50  
  Purchase #4 $73.41   8.362%   $79.5485   $79.55   $79.55   $79.50  
  Purchase #5 $195.47   10.618%   $216.225   $216.23   $216.25   $216.20  
  Purchase #6 $33.64   7.607%   $36.199   $36.20   $36.20   $36.20  
  Purchase #7 $242.88   13.230%   $275.013   $275.01   $275.00   $275.00  
  7 purchase totals = $782.62       $875.0432   $875.05   $875.05   $874.90