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 $56.57   10.774%   $62.6649   $62.66   $62.65   $62.70  
  Purchase #2 $47.35   6.305%   $50.3354   $50.34   $50.35   $50.30  
  Purchase #3 $40.56   6.716%   $43.284   $43.28   $43.30   $43.30  
  Purchase #4 $176.76   11.823%   $197.6583   $197.66   $197.65   $197.70  
  Purchase #5 $201.39   4.604%   $210.662   $210.66   $210.65   $210.70  
  Purchase #6 $159.56   5.699%   $168.6533   $168.65   $168.65   $168.70  
  Purchase #7 $246.52   8.474%   $267.4101   $267.41   $267.40   $267.40  
  7 purchase totals = $928.71       $1,000.6680   $1,000.66   $1,000.65   $1,000.80