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 $227.85   6.121%   $241.7967   $241.80   $241.80   $241.80  
  Purchase #2 $65.60   3.383%   $67.8192   $67.82   $67.80   $67.80  
  Purchase #3 $195.99   5.436%   $206.644   $206.64   $206.65   $206.60  
  Purchase #4 $195.38   6.396%   $207.8765   $207.88   $207.90   $207.90  
  Purchase #5 $157.76   4.475%   $164.8198   $164.82   $164.80   $164.80  
  Purchase #6 $57.92   4.571%   $60.5675   $60.57   $60.55   $60.60  
  Purchase #7 $73.76   9.281%   $80.6057   $80.61   $80.60   $80.60  
  7 purchase totals = $974.26       $1,030.1294   $1,030.14   $1,030.10   $1,030.10