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 $47.91   10.230%   $52.8112   $52.81   $52.80   $52.80  
  Purchase #2 $195.60   5.148%   $205.6695   $205.67   $205.65   $205.70  
  Purchase #3 $42.71   8.799%   $46.4681   $46.47   $46.45   $46.50  
  Purchase #4 $147.58   11.691%   $164.8336   $164.83   $164.85   $164.80  
  Purchase #5 $164.88   7.609%   $177.4257   $177.43   $177.45   $177.40  
  Purchase #6 $128.83   6.396%   $137.07   $137.07   $137.05   $137.10  
  Purchase #7 $240.54   3.264%   $248.3912   $248.39   $248.40   $248.40  
  7 purchase totals = $968.05       $1,032.6693   $1,032.67   $1,032.65   $1,032.70