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 $114.75   13.853%   $130.6463   $130.65   $130.65   $130.60  
  Purchase #2 $86.30   6.233%   $91.6791   $91.68   $91.70   $91.70  
  Purchase #3 $53.67   6.599%   $57.2117   $57.21   $57.20   $57.20  
  Purchase #4 $201.62   12.329%   $226.4777   $226.48   $226.50   $226.50  
  Purchase #5 $135.98   6.533%   $144.8636   $144.86   $144.85   $144.90  
  Purchase #6 $167.40   9.703%   $183.6428   $183.64   $183.65   $183.60  
  Purchase #7 $23.83   12.627%   $26.839   $26.84   $26.85   $26.80  
  7 purchase totals = $783.55       $861.3602   $861.36   $861.40   $861.30