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 $89.28   8.211%   $96.6108   $96.61   $96.60   $96.60  
  Purchase #2 $9.60   6.841%   $10.2567   $10.26   $10.25   $10.30  
  Purchase #3 $180.52   6.548%   $192.3404   $192.34   $192.35   $192.30  
  Purchase #4 $91.28   5.118%   $95.9517   $95.95   $95.95   $96.00  
  Purchase #5 $235.46   6.380%   $250.4823   $250.48   $250.50   $250.50  
  Purchase #6 $209.33   9.441%   $229.0928   $229.09   $229.10   $229.10  
  Purchase #7 $248.61   8.842%   $270.5921   $270.59   $270.60   $270.60  
  7 purchase totals = $1,064.08       $1,145.3268   $1,145.32   $1,145.35   $1,145.40