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 $192.47   7.824%   $207.5289   $207.53   $207.55   $207.50  
  Purchase #2 $119.99   4.534%   $125.4303   $125.43   $125.45   $125.40  
  Purchase #3 $95.43   13.727%   $108.5297   $108.53   $108.55   $108.50  
  Purchase #4 $55.89   12.293%   $62.7606   $62.76   $62.75   $62.80  
  Purchase #5 $184.51   9.161%   $201.413   $201.41   $201.40   $201.40  
  Purchase #6 $108.80   13.785%   $123.7981   $123.80   $123.80   $123.80  
  Purchase #7 $59.65   12.359%   $67.0221   $67.02   $67.00   $67.00  
  7 purchase totals = $816.74       $896.4827   $896.48   $896.50   $896.40