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 $113.46   11.552%   $126.5669   $126.57   $126.55   $126.60  
  Purchase #2 $131.48   11.671%   $146.825   $146.83   $146.85   $146.80  
  Purchase #3 $23.60   7.708%   $25.4191   $25.42   $25.40   $25.40  
  Purchase #4 $111.36   8.421%   $120.7376   $120.74   $120.75   $120.70  
  Purchase #5 $146.87   12.363%   $165.0275   $165.03   $165.05   $165.00  
  Purchase #6 $185.41   10.118%   $204.1698   $204.17   $204.15   $204.20  
  Purchase #7 $5.93   13.469%   $6.7287   $6.73   $6.75   $6.70  
  7 purchase totals = $718.11       $795.4746   $795.49   $795.50   $795.40