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 $94.87   3.136%   $97.8451   $97.85   $97.85   $97.80  
  Purchase #2 $183.25   10.593%   $202.6617   $202.66   $202.65   $202.70  
  Purchase #3 $57.36   10.599%   $63.4396   $63.44   $63.45   $63.40  
  Purchase #4 $16.52   8.662%   $17.951   $17.95   $17.95   $18.00  
  Purchase #5 $56.60   4.186%   $58.9693   $58.97   $58.95   $59.00  
  Purchase #6 $126.40   11.556%   $141.0068   $141.01   $141.00   $141.00  
  Purchase #7 $181.87   11.772%   $203.2797   $203.28   $203.30   $203.30  
  7 purchase totals = $716.87       $785.1532   $785.16   $785.15   $785.20