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 $152.72   6.175%   $162.1505   $162.15   $162.15   $162.20  
  Purchase #2 $177.56   5.711%   $187.7005   $187.70   $187.70   $187.70  
  Purchase #3 $19.96   10.657%   $22.0871   $22.09   $22.10   $22.10  
  Purchase #4 $115.66   5.696%   $122.248   $122.25   $122.25   $122.20  
  Purchase #5 $120.25   8.237%   $130.155   $130.16   $130.15   $130.20  
  Purchase #6 $25.35   11.763%   $28.3319   $28.33   $28.35   $28.30  
  Purchase #7 $181.76   11.516%   $202.6915   $202.69   $202.70   $202.70  
  7 purchase totals = $793.26       $855.3645   $855.37   $855.40   $855.40