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 $59.38   10.575%   $65.6594   $65.66   $65.65   $65.70  
  Purchase #2 $94.27   9.109%   $102.8571   $102.86   $102.85   $102.90  
  Purchase #3 $172.85   6.542%   $184.1578   $184.16   $184.15   $184.20  
  Purchase #4 $199.52   13.137%   $225.7309   $225.73   $225.75   $225.70  
  Purchase #5 $49.67   12.193%   $55.7263   $55.73   $55.75   $55.70  
  Purchase #6 $153.58   13.680%   $174.5897   $174.59   $174.60   $174.60  
  Purchase #7 $165.57   10.617%   $183.1486   $183.15   $183.15   $183.10  
  7 purchase totals = $894.84       $991.8698   $991.88   $991.90   $991.90