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 $176.90   9.522%   $193.7444   $193.74   $193.75   $193.70  
  Purchase #2 $244.40   11.152%   $271.6555   $271.66   $271.65   $271.70  
  Purchase #3 $54.96   7.202%   $58.9182   $58.92   $58.90   $58.90  
  Purchase #4 $250.28   4.104%   $260.5515   $260.55   $260.55   $260.60  
  Purchase #5 $14.47   9.421%   $15.8332   $15.83   $15.85   $15.80  
  Purchase #6 $177.57   4.130%   $184.9036   $184.90   $184.90   $184.90  
  Purchase #7 $31.31   11.655%   $34.9592   $34.96   $34.95   $35.00  
  7 purchase totals = $949.89       $1,020.5656   $1,020.56   $1,020.55   $1,020.60