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 $91.25   8.132%   $98.6705   $98.67   $98.65   $98.70  
  Purchase #2 $154.78   9.499%   $169.4826   $169.48   $169.50   $169.50  
  Purchase #3 $74.63   3.521%   $77.2577   $77.26   $77.25   $77.30  
  Purchase #4 $187.97   3.746%   $195.0114   $195.01   $195.00   $195.00  
  Purchase #5 $155.41   13.231%   $175.9723   $175.97   $175.95   $176.00  
  Purchase #6 $97.54   11.841%   $109.0897   $109.09   $109.10   $109.10  
  Purchase #7 $235.68   3.470%   $243.8581   $243.86   $243.85   $243.90  
  7 purchase totals = $997.26       $1,069.3423   $1,069.34   $1,069.30   $1,069.50