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 $156.77   4.560%   $163.9187   $163.92   $163.90   $163.90  
  Purchase #2 $39.81   4.851%   $41.7412   $41.74   $41.75   $41.70  
  Purchase #3 $179.91   4.624%   $188.229   $188.23   $188.25   $188.20  
  Purchase #4 $53.25   8.205%   $57.6192   $57.62   $57.60   $57.60  
  Purchase #5 $64.72   9.605%   $70.9364   $70.94   $70.95   $70.90  
  Purchase #6 $179.55   4.302%   $187.2742   $187.27   $187.25   $187.30  
  Purchase #7 $211.28   9.266%   $230.8572   $230.86   $230.85   $230.90  
  7 purchase totals = $885.29       $940.5759   $940.58   $940.55   $940.50