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 $177.56   3.202%   $183.2455   $183.25   $183.25   $183.20  
  Purchase #2 $223.77   7.832%   $241.2957   $241.30   $241.30   $241.30  
  Purchase #3 $206.31   6.154%   $219.0063   $219.01   $219.00   $219.00  
  Purchase #4 $23.56   12.655%   $26.5415   $26.54   $26.55   $26.50  
  Purchase #5 $177.98   8.770%   $193.5888   $193.59   $193.60   $193.60  
  Purchase #6 $73.65   4.649%   $77.074   $77.07   $77.05   $77.10  
  Purchase #7 $94.76   7.148%   $101.5334   $101.53   $101.55   $101.50  
  7 purchase totals = $977.59       $1,042.2852   $1,042.29   $1,042.30   $1,042.20