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 $241.55   6.738%   $257.8256   $257.83   $257.85   $257.80  
  Purchase #2 $59.81   11.258%   $66.5434   $66.54   $66.55   $66.50  
  Purchase #3 $172.72   11.474%   $192.5379   $192.54   $192.55   $192.50  
  Purchase #4 $186.74   7.645%   $201.0163   $201.02   $201.00   $201.00  
  Purchase #5 $204.69   13.553%   $232.4316   $232.43   $232.45   $232.40  
  Purchase #6 $208.36   12.451%   $234.3029   $234.30   $234.30   $234.30  
  Purchase #7 $167.25   5.264%   $176.054   $176.05   $176.05   $176.10  
  7 purchase totals = $1,241.12       $1,360.7117   $1,360.71   $1,360.75   $1,360.60