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 $59.44   9.240%   $64.9323   $64.93   $64.95   $64.90  
  Purchase #2 $73.89   9.674%   $81.0381   $81.04   $81.05   $81.00  
  Purchase #3 $224.61   10.795%   $248.8566   $248.86   $248.85   $248.90  
  Purchase #4 $194.75   8.542%   $211.3855   $211.39   $211.40   $211.40  
  Purchase #5 $179.96   11.723%   $201.0567   $201.06   $201.05   $201.10  
  Purchase #6 $123.66   6.404%   $131.5792   $131.58   $131.60   $131.60  
  Purchase #7 $38.69   9.303%   $42.2893   $42.29   $42.30   $42.30  
  7 purchase totals = $895.00       $981.1377   $981.15   $981.20   $981.20