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 $186.52   7.758%   $200.9902   $200.99   $201.00   $201.00  
  Purchase #2 $50.93   6.117%   $54.0454   $54.05   $54.05   $54.00  
  Purchase #3 $78.37   4.689%   $82.0448   $82.04   $82.05   $82.00  
  Purchase #4 $201.33   12.267%   $226.0272   $226.03   $226.05   $226.00  
  Purchase #5 $165.47   10.336%   $182.573   $182.57   $182.55   $182.60  
  Purchase #6 $246.77   10.376%   $272.3749   $272.37   $272.35   $272.40  
  Purchase #7 $152.83   5.495%   $161.228   $161.23   $161.25   $161.20  
  7 purchase totals = $1,082.22       $1,179.2835   $1,179.28   $1,179.30   $1,179.20