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 $11.29   6.528%   $12.027   $12.03   $12.05   $12.00  
  Purchase #2 $80.53   12.417%   $90.5294   $90.53   $90.55   $90.50  
  Purchase #3 $132.95   5.389%   $140.1147   $140.11   $140.10   $140.10  
  Purchase #4 $151.67   6.605%   $161.6878   $161.69   $161.70   $161.70  
  Purchase #5 $120.91   6.581%   $128.8671   $128.87   $128.85   $128.90  
  Purchase #6 $156.54   11.686%   $174.8333   $174.83   $174.85   $174.80  
  Purchase #7 $41.94   12.402%   $47.1414   $47.14   $47.15   $47.10  
  7 purchase totals = $695.83       $755.2007   $755.20   $755.25   $755.10