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 $90.67   7.579%   $97.5419   $97.54   $97.55   $97.50  
  Purchase #2 $14.81   9.179%   $16.1694   $16.17   $16.15   $16.20  
  Purchase #3 $194.54   4.696%   $203.6756   $203.68   $203.70   $203.70  
  Purchase #4 $154.32   7.235%   $165.4851   $165.49   $165.50   $165.50  
  Purchase #5 $158.87   4.505%   $166.0271   $166.03   $166.05   $166.00  
  Purchase #6 $88.33   12.149%   $99.0612   $99.06   $99.05   $99.10  
  Purchase #7 $164.28   9.520%   $179.9195   $179.92   $179.90   $179.90  
  7 purchase totals = $865.82       $927.8798   $927.89   $927.90   $927.90