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 $151.36   5.483%   $159.6591   $159.66   $159.65   $159.70  
  Purchase #2 $124.28   10.146%   $136.8894   $136.89   $136.90   $136.90  
  Purchase #3 $77.46   8.420%   $83.9821   $83.98   $84.00   $84.00  
  Purchase #4 $151.90   5.580%   $160.376   $160.38   $160.40   $160.40  
  Purchase #5 $231.69   11.870%   $259.1916   $259.19   $259.20   $259.20  
  Purchase #6 $60.57   6.653%   $64.5997   $64.60   $64.60   $64.60  
  Purchase #7 $220.46   12.560%   $248.1498   $248.15   $248.15   $248.10  
  7 purchase totals = $1,017.72       $1,112.8477   $1,112.85   $1,112.90   $1,112.90