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 $162.60   8.455%   $176.3478   $176.35   $176.35   $176.30  
  Purchase #2 $35.90   8.396%   $38.9142   $38.91   $38.90   $38.90  
  Purchase #3 $193.43   8.438%   $209.7516   $209.75   $209.75   $209.80  
  Purchase #4 $227.39   6.257%   $241.6178   $241.62   $241.60   $241.60  
  Purchase #5 $95.58   13.773%   $108.7442   $108.74   $108.75   $108.70  
  Purchase #6 $93.89   12.452%   $105.5812   $105.58   $105.60   $105.60  
  Purchase #7 $186.85   7.584%   $201.0207   $201.02   $201.00   $201.00  
  7 purchase totals = $995.64       $1,081.9775   $1,081.97   $1,081.95   $1,081.90