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 $14.71   11.729%   $16.4353   $16.44   $16.45   $16.40  
  Purchase #2 $63.33   3.162%   $65.3325   $65.33   $65.35   $65.30  
  Purchase #3 $189.45   6.611%   $201.9745   $201.97   $201.95   $202.00  
  Purchase #4 $95.59   13.783%   $108.7652   $108.77   $108.75   $108.80  
  Purchase #5 $156.36   6.499%   $166.5218   $166.52   $166.50   $166.50  
  Purchase #6 $182.90   9.661%   $200.57   $200.57   $200.55   $200.60  
  Purchase #7 $109.81   4.549%   $114.8053   $114.81   $114.80   $114.80  
  7 purchase totals = $812.15       $874.4046   $874.41   $874.35   $874.40