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 $20.84   5.529%   $21.9922   $21.99   $22.00   $22.00  
  Purchase #2 $5.54   5.252%   $5.831   $5.83   $5.85   $5.80  
  Purchase #3 $20.47   11.456%   $22.815   $22.82   $22.80   $22.80  
  Purchase #4 $156.62   6.419%   $166.6734   $166.67   $166.65   $166.70  
  Purchase #5 $109.39   13.723%   $124.4016   $124.40   $124.40   $124.40  
  Purchase #6 $94.97   4.574%   $99.3139   $99.31   $99.30   $99.30  
  Purchase #7 $111.86   8.857%   $121.7674   $121.77   $121.75   $121.80  
  7 purchase totals = $519.69       $562.7945   $562.79   $562.75   $562.80