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 $35.71   3.144%   $36.8327   $36.83   $36.85   $36.80  
  Purchase #2 $230.80   12.183%   $258.9184   $258.92   $258.90   $258.90  
  Purchase #3 $177.39   8.558%   $192.571   $192.57   $192.55   $192.60  
  Purchase #4 $140.46   3.409%   $145.2483   $145.25   $145.25   $145.20  
  Purchase #5 $247.33   13.778%   $281.4071   $281.41   $281.40   $281.40  
  Purchase #6 $69.57   3.503%   $72.007   $72.01   $72.00   $72.00  
  Purchase #7 $153.70   9.102%   $167.6898   $167.69   $167.70   $167.70  
  7 purchase totals = $1,054.96       $1,154.6743   $1,154.68   $1,154.65   $1,154.60