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 $185.71   4.137%   $193.3928   $193.39   $193.40   $193.40  
  Purchase #2 $173.87   7.117%   $186.2443   $186.24   $186.25   $186.20  
  Purchase #3 $141.46   8.874%   $154.0132   $154.01   $154.00   $154.00  
  Purchase #4 $54.93   8.225%   $59.448   $59.45   $59.45   $59.40  
  Purchase #5 $100.44   5.605%   $106.0697   $106.07   $106.05   $106.10  
  Purchase #6 $165.68   5.290%   $174.4445   $174.44   $174.45   $174.40  
  Purchase #7 $40.30   11.802%   $45.0562   $45.06   $45.05   $45.10  
  7 purchase totals = $862.39       $918.6687   $918.66   $918.65   $918.60