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 $243.30   10.613%   $269.1214   $269.12   $269.10   $269.10  
  Purchase #2 $194.59   12.356%   $218.6335   $218.63   $218.65   $218.60  
  Purchase #3 $80.93   6.224%   $85.9671   $85.97   $85.95   $86.00  
  Purchase #4 $152.28   12.844%   $171.8388   $171.84   $171.85   $171.80  
  Purchase #5 $139.89   11.220%   $155.5857   $155.59   $155.60   $155.60  
  Purchase #6 $224.59   6.589%   $239.3882   $239.39   $239.40   $239.40  
  Purchase #7 $214.97   13.247%   $243.4471   $243.45   $243.45   $243.40  
  7 purchase totals = $1,250.55       $1,383.9818   $1,383.99   $1,384.00   $1,383.90