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 $138.25   10.164%   $152.3017   $152.30   $152.30   $152.30  
  Purchase #2 $110.97   7.288%   $119.0575   $119.06   $119.05   $119.10  
  Purchase #3 $51.93   3.311%   $53.6494   $53.65   $53.65   $53.60  
  Purchase #4 $72.97   13.227%   $82.6217   $82.62   $82.60   $82.60  
  Purchase #5 $188.88   9.385%   $206.6064   $206.61   $206.60   $206.60  
  Purchase #6 $244.92   5.273%   $257.8346   $257.83   $257.85   $257.80  
  Purchase #7 $236.66   11.385%   $263.6037   $263.60   $263.60   $263.60  
  7 purchase totals = $1,044.58       $1,135.6750   $1,135.67   $1,135.65   $1,135.60