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 $73.63   11.522%   $82.1136   $82.11   $82.10   $82.10  
  Purchase #2 $181.90   6.147%   $193.0814   $193.08   $193.10   $193.10  
  Purchase #3 $70.87   11.864%   $79.278   $79.28   $79.30   $79.30  
  Purchase #4 $223.28   5.272%   $235.0513   $235.05   $235.05   $235.10  
  Purchase #5 $208.80   9.614%   $228.874   $228.87   $228.85   $228.90  
  Purchase #6 $201.80   12.441%   $226.9059   $226.91   $226.90   $226.90  
  Purchase #7 $242.91   5.340%   $255.8814   $255.88   $255.90   $255.90  
  7 purchase totals = $1,203.19       $1,301.1856   $1,301.18   $1,301.20   $1,301.30