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 $165.87   10.766%   $183.7276   $183.73   $183.75   $183.70  
  Purchase #2 $33.55   13.155%   $37.9635   $37.96   $37.95   $38.00  
  Purchase #3 $22.48   8.155%   $24.3132   $24.31   $24.30   $24.30  
  Purchase #4 $49.28   3.815%   $51.16   $51.16   $51.15   $51.20  
  Purchase #5 $47.25   7.339%   $50.7177   $50.72   $50.70   $50.70  
  Purchase #6 $228.38   13.198%   $258.5216   $258.52   $258.50   $258.50  
  Purchase #7 $83.87   11.330%   $93.3725   $93.37   $93.35   $93.40  
  7 purchase totals = $630.68       $699.7761   $699.77   $699.70   $699.80