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 $148.51   12.293%   $166.7663   $166.77   $166.75   $166.80  
  Purchase #2 $65.93   6.730%   $70.3671   $70.37   $70.35   $70.40  
  Purchase #3 $225.95   8.249%   $244.5886   $244.59   $244.60   $244.60  
  Purchase #4 $65.56   11.581%   $73.1525   $73.15   $73.15   $73.20  
  Purchase #5 $55.61   10.842%   $61.6392   $61.64   $61.65   $61.60  
  Purchase #6 $146.66   10.831%   $162.5447   $162.54   $162.55   $162.50  
  Purchase #7 $228.89   9.224%   $250.0028   $250.00   $250.00   $250.00  
  7 purchase totals = $937.11       $1,029.0612   $1,029.06   $1,029.05   $1,029.10