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 $245.25   11.677%   $273.8878   $273.89   $273.90   $273.90  
  Purchase #2 $5.90   13.425%   $6.6921   $6.69   $6.70   $6.70  
  Purchase #3 $244.74   13.169%   $276.9698   $276.97   $276.95   $277.00  
  Purchase #4 $95.36   9.124%   $104.0606   $104.06   $104.05   $104.10  
  Purchase #5 $99.88   9.342%   $109.2108   $109.21   $109.20   $109.20  
  Purchase #6 $114.62   4.278%   $119.5234   $119.52   $119.50   $119.50  
  Purchase #7 $203.53   12.287%   $228.5377   $228.54   $228.55   $228.50  
  7 purchase totals = $1,009.28       $1,118.8822   $1,118.88   $1,118.85   $1,118.90