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 $11.83   5.164%   $12.4409   $12.44   $12.45   $12.40  
  Purchase #2 $200.78   12.338%   $225.5522   $225.55   $225.55   $225.60  
  Purchase #3 $234.84   10.303%   $259.0356   $259.04   $259.05   $259.00  
  Purchase #4 $233.52   6.369%   $248.3929   $248.39   $248.40   $248.40  
  Purchase #5 $177.43   7.479%   $190.7   $190.70   $190.70   $190.70  
  Purchase #6 $25.47   3.341%   $26.321   $26.32   $26.30   $26.30  
  Purchase #7 $242.39   9.110%   $264.4717   $264.47   $264.45   $264.50  
  7 purchase totals = $1,126.26       $1,226.9143   $1,226.91   $1,226.90   $1,226.90