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 $126.66   3.173%   $130.6789   $130.68   $130.70   $130.70  
  Purchase #2 $22.75   7.324%   $24.4162   $24.42   $24.40   $24.40  
  Purchase #3 $80.87   9.572%   $88.6109   $88.61   $88.60   $88.60  
  Purchase #4 $144.39   4.852%   $151.3958   $151.40   $151.40   $151.40  
  Purchase #5 $38.88   7.289%   $41.714   $41.71   $41.70   $41.70  
  Purchase #6 $122.61   11.576%   $136.8033   $136.80   $136.80   $136.80  
  Purchase #7 $165.85   10.701%   $183.5976   $183.60   $183.60   $183.60  
  7 purchase totals = $702.01       $757.2167   $757.22   $757.20   $757.20