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 $53.65   7.474%   $57.6598   $57.66   $57.65   $57.70  
  Purchase #2 $244.63   10.114%   $269.3719   $269.37   $269.35   $269.40  
  Purchase #3 $219.48   4.110%   $228.5006   $228.50   $228.50   $228.50  
  Purchase #4 $98.26   10.787%   $108.8593   $108.86   $108.85   $108.90  
  Purchase #5 $119.87   5.203%   $126.1068   $126.11   $126.10   $126.10  
  Purchase #6 $137.45   9.234%   $150.1421   $150.14   $150.15   $150.10  
  Purchase #7 $183.41   8.371%   $198.7633   $198.76   $198.75   $198.80  
  7 purchase totals = $1,056.75       $1,139.4038   $1,139.40   $1,139.35   $1,139.50