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 $161.61   3.139%   $166.6829   $166.68   $166.70   $166.70  
  Purchase #2 $227.94   9.109%   $248.7031   $248.70   $248.70   $248.70  
  Purchase #3 $45.79   13.459%   $51.9529   $51.95   $51.95   $52.00  
  Purchase #4 $205.42   11.819%   $229.6986   $229.70   $229.70   $229.70  
  Purchase #5 $238.62   8.533%   $258.9814   $258.98   $259.00   $259.00  
  Purchase #6 $156.72   6.132%   $166.3301   $166.33   $166.35   $166.30  
  Purchase #7 $220.92   8.368%   $239.4066   $239.41   $239.40   $239.40  
  7 purchase totals = $1,257.02       $1,361.7556   $1,361.75   $1,361.80   $1,361.80