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 $109.37   5.546%   $115.4357   $115.44   $115.45   $115.40  
  Purchase #2 $102.36   6.583%   $109.0984   $109.10   $109.10   $109.10  
  Purchase #3 $140.42   9.702%   $154.0435   $154.04   $154.05   $154.00  
  Purchase #4 $149.47   10.442%   $165.0777   $165.08   $165.10   $165.10  
  Purchase #5 $47.69   8.332%   $51.6635   $51.66   $51.65   $51.70  
  Purchase #6 $63.97   3.767%   $66.3797   $66.38   $66.40   $66.40  
  Purchase #7 $63.37   11.855%   $70.8825   $70.88   $70.90   $70.90  
  7 purchase totals = $676.65       $732.5810   $732.58   $732.65   $732.60