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 $228.88   8.356%   $248.0052   $248.01   $248.00   $248.00  
  Purchase #2 $55.28   8.248%   $59.8395   $59.84   $59.85   $59.80  
  Purchase #3 $177.51   5.736%   $187.692   $187.69   $187.70   $187.70  
  Purchase #4 $63.80   13.344%   $72.3135   $72.31   $72.30   $72.30  
  Purchase #5 $191.36   12.256%   $214.8131   $214.81   $214.80   $214.80  
  Purchase #6 $57.91   8.252%   $62.6887   $62.69   $62.70   $62.70  
  Purchase #7 $99.52   4.211%   $103.7108   $103.71   $103.70   $103.70  
  7 purchase totals = $874.26       $949.0628   $949.06   $949.05   $949.00