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 $61.85   12.498%   $69.58   $69.58   $69.60   $69.60  
  Purchase #2 $186.27   11.447%   $207.5923   $207.59   $207.60   $207.60  
  Purchase #3 $22.72   12.433%   $25.5448   $25.54   $25.55   $25.50  
  Purchase #4 $102.76   10.558%   $113.6094   $113.61   $113.60   $113.60  
  Purchase #5 $31.70   12.310%   $35.6023   $35.60   $35.60   $35.60  
  Purchase #6 $46.34   11.358%   $51.6033   $51.60   $51.60   $51.60  
  Purchase #7 $118.64   6.627%   $126.5023   $126.50   $126.50   $126.50  
  7 purchase totals = $570.28       $630.0344   $630.02   $630.05   $630.00