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 $55.88   7.621%   $60.1386   $60.14   $60.15   $60.10  
  Purchase #2 $247.66   8.723%   $269.2634   $269.26   $269.25   $269.30  
  Purchase #3 $84.79   12.531%   $95.415   $95.42   $95.40   $95.40  
  Purchase #4 $140.59   8.778%   $152.931   $152.93   $152.95   $152.90  
  Purchase #5 $173.35   10.182%   $191.0005   $191.00   $191.00   $191.00  
  Purchase #6 $195.29   3.162%   $201.4651   $201.47   $201.45   $201.50  
  Purchase #7 $225.47   9.474%   $246.831   $246.83   $246.85   $246.80  
  7 purchase totals = $1,123.03       $1,217.0446   $1,217.05   $1,217.05   $1,217.00