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 $88.35   12.842%   $99.6959   $99.70   $99.70   $99.70  
  Purchase #2 $106.25   3.208%   $109.6585   $109.66   $109.65   $109.70  
  Purchase #3 $162.89   13.284%   $184.5283   $184.53   $184.55   $184.50  
  Purchase #4 $237.71   8.137%   $257.0525   $257.05   $257.05   $257.10  
  Purchase #5 $23.38   9.762%   $25.6624   $25.66   $25.65   $25.70  
  Purchase #6 $33.33   6.866%   $35.6184   $35.62   $35.60   $35.60  
  Purchase #7 $212.68   7.860%   $229.3966   $229.40   $229.40   $229.40  
  7 purchase totals = $864.59       $941.6126   $941.62   $941.60   $941.70