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 $62.59   4.162%   $65.195   $65.20   $65.20   $65.20  
  Purchase #2 $69.98   8.163%   $75.6925   $75.69   $75.70   $75.70  
  Purchase #3 $223.75   10.194%   $246.5591   $246.56   $246.55   $246.60  
  Purchase #4 $114.26   6.582%   $121.7806   $121.78   $121.80   $121.80  
  Purchase #5 $54.34   5.301%   $57.2206   $57.22   $57.20   $57.20  
  Purchase #6 $134.59   11.494%   $150.0598   $150.06   $150.05   $150.10  
  Purchase #7 $71.66   8.131%   $77.4867   $77.49   $77.50   $77.50  
  7 purchase totals = $731.17       $793.9943   $794.00   $794.00   $794.10