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 $234.87   10.839%   $260.3276   $260.33   $260.35   $260.30  
  Purchase #2 $216.99   7.830%   $233.9803   $233.98   $234.00   $234.00  
  Purchase #3 $54.80   10.411%   $60.5052   $60.51   $60.50   $60.50  
  Purchase #4 $231.59   11.254%   $257.6531   $257.65   $257.65   $257.70  
  Purchase #5 $151.42   7.109%   $162.1844   $162.18   $162.20   $162.20  
  Purchase #6 $69.83   11.188%   $77.6426   $77.64   $77.65   $77.60  
  Purchase #7 $27.55   5.588%   $29.0895   $29.09   $29.10   $29.10  
  7 purchase totals = $987.05       $1,081.3827   $1,081.38   $1,081.45   $1,081.40