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 $23.33   11.134%   $25.9276   $25.93   $25.95   $25.90  
  Purchase #2 $116.41   7.123%   $124.7019   $124.70   $124.70   $124.70  
  Purchase #3 $12.53   11.413%   $13.96   $13.96   $13.95   $14.00  
  Purchase #4 $25.81   7.323%   $27.7001   $27.70   $27.70   $27.70  
  Purchase #5 $117.76   3.134%   $121.4506   $121.45   $121.45   $121.50  
  Purchase #6 $32.56   9.709%   $35.7213   $35.72   $35.70   $35.70  
  Purchase #7 $211.62   7.217%   $226.8926   $226.89   $226.90   $226.90  
  7 purchase totals = $540.02       $576.3541   $576.35   $576.35   $576.40