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 $155.66   6.555%   $165.8635   $165.86   $165.85   $165.90  
  Purchase #2 $126.89   10.281%   $139.9356   $139.94   $139.95   $139.90  
  Purchase #3 $135.72   10.503%   $149.9747   $149.97   $149.95   $150.00  
  Purchase #4 $246.87   3.292%   $254.997   $255.00   $255.00   $255.00  
  Purchase #5 $177.99   4.236%   $185.5297   $185.53   $185.55   $185.50  
  Purchase #6 $156.50   5.306%   $164.8039   $164.80   $164.80   $164.80  
  Purchase #7 $49.55   3.603%   $51.3353   $51.34   $51.35   $51.30  
  7 purchase totals = $1,049.18       $1,112.4397   $1,112.44   $1,112.45   $1,112.40