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 $61.58   3.109%   $63.4945   $63.49   $63.50   $63.50  
  Purchase #2 $206.26   4.637%   $215.8243   $215.82   $215.80   $215.80  
  Purchase #3 $126.67   12.149%   $142.0591   $142.06   $142.05   $142.10  
  Purchase #4 $75.51   9.372%   $82.5868   $82.59   $82.60   $82.60  
  Purchase #5 $199.74   10.800%   $221.3119   $221.31   $221.30   $221.30  
  Purchase #6 $22.28   11.856%   $24.9215   $24.92   $24.90   $24.90  
  Purchase #7 $145.98   6.323%   $155.2103   $155.21   $155.20   $155.20  
  7 purchase totals = $838.02       $905.4084   $905.40   $905.35   $905.40