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 $55.61   11.126%   $61.7972   $61.80   $61.80   $61.80  
  Purchase #2 $150.94   6.874%   $161.3156   $161.32   $161.30   $161.30  
  Purchase #3 $197.80   12.524%   $222.5725   $222.57   $222.55   $222.60  
  Purchase #4 $212.68   4.732%   $222.744   $222.74   $222.75   $222.70  
  Purchase #5 $119.27   3.717%   $123.7033   $123.70   $123.70   $123.70  
  Purchase #6 $146.92   13.104%   $166.1724   $166.17   $166.15   $166.20  
  Purchase #7 $122.80   10.178%   $135.2986   $135.30   $135.30   $135.30  
  7 purchase totals = $1,006.02       $1,093.6036   $1,093.60   $1,093.55   $1,093.60