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 $88.89   4.216%   $92.6376   $92.64   $92.65   $92.60  
  Purchase #2 $196.59   9.298%   $214.8689   $214.87   $214.85   $214.90  
  Purchase #3 $86.54   13.355%   $98.0974   $98.10   $98.10   $98.10  
  Purchase #4 $61.37   11.795%   $68.6086   $68.61   $68.60   $68.60  
  Purchase #5 $151.44   10.169%   $166.8399   $166.84   $166.85   $166.80  
  Purchase #6 $151.25   10.142%   $166.5898   $166.59   $166.60   $166.60  
  Purchase #7 $208.32   7.531%   $224.0086   $224.01   $224.00   $224.00  
  7 purchase totals = $944.40       $1,031.6508   $1,031.66   $1,031.65   $1,031.60