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 $90.57   8.151%   $97.9524   $97.95   $97.95   $98.00  
  Purchase #2 $56.65   6.185%   $60.1538   $60.15   $60.15   $60.20  
  Purchase #3 $36.42   11.651%   $40.6633   $40.66   $40.65   $40.70  
  Purchase #4 $192.27   7.535%   $206.7575   $206.76   $206.75   $206.80  
  Purchase #5 $82.60   9.711%   $90.6213   $90.62   $90.60   $90.60  
  Purchase #6 $201.66   8.813%   $219.4323   $219.43   $219.45   $219.40  
  Purchase #7 $77.75   8.252%   $84.1659   $84.17   $84.15   $84.20  
  7 purchase totals = $737.92       $799.7465   $799.74   $799.70   $799.90