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 $205.80   13.463%   $233.5069   $233.51   $233.50   $233.50  
  Purchase #2 $45.85   13.522%   $52.0498   $52.05   $52.05   $52.00  
  Purchase #3 $155.67   11.738%   $173.9425   $173.94   $173.95   $173.90  
  Purchase #4 $14.72   13.270%   $16.6733   $16.67   $16.65   $16.70  
  Purchase #5 $198.68   11.348%   $221.2262   $221.23   $221.25   $221.20  
  Purchase #6 $154.52   8.320%   $167.3761   $167.38   $167.40   $167.40  
  Purchase #7 $28.49   9.354%   $31.155   $31.16   $31.15   $31.20  
  7 purchase totals = $803.73       $895.9298   $895.94   $895.95   $895.90