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 $65.72   5.721%   $69.4798   $69.48   $69.50   $69.50  
  Purchase #2 $132.45   5.451%   $139.6698   $139.67   $139.65   $139.70  
  Purchase #3 $168.97   12.851%   $190.6843   $190.68   $190.70   $190.70  
  Purchase #4 $199.81   9.444%   $218.6801   $218.68   $218.70   $218.70  
  Purchase #5 $241.52   7.693%   $260.1001   $260.10   $260.10   $260.10  
  Purchase #6 $110.77   13.824%   $126.0828   $126.08   $126.10   $126.10  
  Purchase #7 $42.28   3.444%   $43.7361   $43.74   $43.75   $43.70  
  7 purchase totals = $961.52       $1,048.4330   $1,048.43   $1,048.50   $1,048.50