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 $60.45   6.866%   $64.6005   $64.60   $64.60   $64.60  
  Purchase #2 $173.48   10.428%   $191.5705   $191.57   $191.55   $191.60  
  Purchase #3 $25.67   5.688%   $27.1301   $27.13   $27.15   $27.10  
  Purchase #4 $110.68   3.713%   $114.7895   $114.79   $114.80   $114.80  
  Purchase #5 $144.27   11.465%   $160.8106   $160.81   $160.80   $160.80  
  Purchase #6 $148.49   5.472%   $156.6154   $156.62   $156.60   $156.60  
  Purchase #7 $182.87   10.153%   $201.4368   $201.44   $201.45   $201.40  
  7 purchase totals = $845.91       $916.9534   $916.96   $916.95   $916.90