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 $80.93   4.669%   $84.7086   $84.71   $84.70   $84.70  
  Purchase #2 $43.32   13.586%   $49.2055   $49.21   $49.20   $49.20  
  Purchase #3 $175.86   10.253%   $193.8909   $193.89   $193.90   $193.90  
  Purchase #4 $241.61   6.423%   $257.1286   $257.13   $257.15   $257.10  
  Purchase #5 $126.67   8.441%   $137.3622   $137.36   $137.35   $137.40  
  Purchase #6 $116.45   6.334%   $123.8259   $123.83   $123.85   $123.80  
  Purchase #7 $149.77   12.272%   $168.1498   $168.15   $168.15   $168.10  
  7 purchase totals = $934.61       $1,014.2715   $1,014.28   $1,014.30   $1,014.20