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 $194.36   4.848%   $203.7826   $203.78   $203.80   $203.80  
  Purchase #2 $60.94   8.144%   $65.903   $65.90   $65.90   $65.90  
  Purchase #3 $169.93   7.712%   $183.035   $183.04   $183.05   $183.00  
  Purchase #4 $47.85   5.335%   $50.4028   $50.40   $50.40   $50.40  
  Purchase #5 $22.73   12.172%   $25.4967   $25.50   $25.50   $25.50  
  Purchase #6 $142.64   6.665%   $152.147   $152.15   $152.15   $152.10  
  Purchase #7 $181.39   13.700%   $206.2404   $206.24   $206.25   $206.20  
  7 purchase totals = $819.84       $887.0075   $887.01   $887.05   $886.90