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 $94.34   4.707%   $98.7806   $98.78   $98.80   $98.80  
  Purchase #2 $98.61   4.302%   $102.8522   $102.85   $102.85   $102.90  
  Purchase #3 $67.69   13.142%   $76.5858   $76.59   $76.60   $76.60  
  Purchase #4 $149.87   9.116%   $163.5321   $163.53   $163.55   $163.50  
  Purchase #5 $94.28   13.874%   $107.3604   $107.36   $107.35   $107.40  
  Purchase #6 $131.90   8.373%   $142.944   $142.94   $142.95   $142.90  
  Purchase #7 $146.47   13.331%   $165.9959   $166.00   $166.00   $166.00  
  7 purchase totals = $783.16       $858.0510   $858.05   $858.10   $858.10