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 $169.93   9.486%   $186.0496   $186.05   $186.05   $186.00  
  Purchase #2 $142.25   6.351%   $151.2843   $151.28   $151.30   $151.30  
  Purchase #3 $22.63   3.809%   $23.492   $23.49   $23.50   $23.50  
  Purchase #4 $33.83   8.692%   $36.7705   $36.77   $36.75   $36.80  
  Purchase #5 $97.46   5.483%   $102.8037   $102.80   $102.80   $102.80  
  Purchase #6 $195.84   9.421%   $214.2901   $214.29   $214.30   $214.30  
  Purchase #7 $165.53   8.653%   $179.8533   $179.85   $179.85   $179.90  
  7 purchase totals = $827.47       $894.5435   $894.53   $894.55   $894.60