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 $98.29   5.859%   $104.0488   $104.05   $104.05   $104.00  
  Purchase #2 $179.43   11.369%   $199.8294   $199.83   $199.85   $199.80  
  Purchase #3 $165.92   11.584%   $185.1402   $185.14   $185.15   $185.10  
  Purchase #4 $54.92   12.678%   $61.8828   $61.88   $61.90   $61.90  
  Purchase #5 $186.50   13.680%   $212.0132   $212.01   $212.00   $212.00  
  Purchase #6 $237.41   5.689%   $250.9163   $250.92   $250.90   $250.90  
  Purchase #7 $149.75   7.305%   $160.6892   $160.69   $160.70   $160.70  
  7 purchase totals = $1,072.22       $1,174.5199   $1,174.52   $1,174.55   $1,174.40