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 $58.93   3.166%   $60.7957   $60.80   $60.80   $60.80  
  Purchase #2 $211.64   4.424%   $221.003   $221.00   $221.00   $221.00  
  Purchase #3 $67.35   6.259%   $71.5654   $71.57   $71.55   $71.60  
  Purchase #4 $161.45   9.345%   $176.5375   $176.54   $176.55   $176.50  
  Purchase #5 $65.50   9.228%   $71.5443   $71.54   $71.55   $71.50  
  Purchase #6 $237.41   10.717%   $262.8532   $262.85   $262.85   $262.90  
  Purchase #7 $118.36   6.705%   $126.296   $126.30   $126.30   $126.30  
  7 purchase totals = $920.64       $990.5951   $990.60   $990.60   $990.60