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 $213.82   13.348%   $242.3607   $242.36   $242.35   $242.40  
  Purchase #2 $157.65   10.324%   $173.9258   $173.93   $173.95   $173.90  
  Purchase #3 $56.87   10.747%   $62.9818   $62.98   $63.00   $63.00  
  Purchase #4 $156.98   5.220%   $165.1744   $165.17   $165.15   $165.20  
  Purchase #5 $166.48   7.873%   $179.587   $179.59   $179.60   $179.60  
  Purchase #6 $217.54   6.717%   $232.1522   $232.15   $232.15   $232.20  
  Purchase #7 $112.58   13.727%   $128.0339   $128.03   $128.05   $128.00  
  7 purchase totals = $1,081.92       $1,184.2158   $1,184.21   $1,184.25   $1,184.30