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 $144.66   11.770%   $161.6865   $161.69   $161.70   $161.70  
  Purchase #2 $138.26   9.862%   $151.8952   $151.90   $151.90   $151.90  
  Purchase #3 $137.53   3.379%   $142.1771   $142.18   $142.20   $142.20  
  Purchase #4 $224.68   11.351%   $250.1834   $250.18   $250.20   $250.20  
  Purchase #5 $175.52   6.183%   $186.3724   $186.37   $186.35   $186.40  
  Purchase #6 $54.82   11.258%   $60.9916   $60.99   $61.00   $61.00  
  Purchase #7 $77.26   5.467%   $81.4838   $81.48   $81.50   $81.50  
  7 purchase totals = $952.73       $1,034.7900   $1,034.79   $1,034.85   $1,034.90