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 $93.81   11.159%   $104.2783   $104.28   $104.30   $104.30  
  Purchase #2 $243.89   8.654%   $264.9962   $265.00   $265.00   $265.00  
  Purchase #3 $147.36   9.231%   $160.9628   $160.96   $160.95   $161.00  
  Purchase #4 $93.80   8.268%   $101.5554   $101.56   $101.55   $101.60  
  Purchase #5 $200.52   3.664%   $207.8671   $207.87   $207.85   $207.90  
  Purchase #6 $68.55   8.641%   $74.4734   $74.47   $74.45   $74.50  
  Purchase #7 $79.79   6.839%   $85.2468   $85.25   $85.25   $85.20  
  7 purchase totals = $927.72       $999.3800   $999.39   $999.35   $999.50