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 $36.51   13.623%   $41.4838   $41.48   $41.50   $41.50  
  Purchase #2 $148.57   12.164%   $166.6421   $166.64   $166.65   $166.60  
  Purchase #3 $115.98   5.776%   $122.679   $122.68   $122.70   $122.70  
  Purchase #4 $31.93   5.301%   $33.6226   $33.62   $33.60   $33.60  
  Purchase #5 $241.77   6.306%   $257.016   $257.02   $257.00   $257.00  
  Purchase #6 $220.89   5.522%   $233.0875   $233.09   $233.10   $233.10  
  Purchase #7 $102.45   4.613%   $107.176   $107.18   $107.20   $107.20  
  7 purchase totals = $898.10       $961.7070   $961.71   $961.75   $961.70