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 $22.98   11.732%   $25.676   $25.68   $25.70   $25.70  
  Purchase #2 $131.49   12.186%   $147.5134   $147.51   $147.50   $147.50  
  Purchase #3 $179.28   10.769%   $198.5867   $198.59   $198.60   $198.60  
  Purchase #4 $246.44   10.241%   $271.6779   $271.68   $271.70   $271.70  
  Purchase #5 $192.85   12.371%   $216.7075   $216.71   $216.70   $216.70  
  Purchase #6 $204.45   3.321%   $211.2398   $211.24   $211.25   $211.20  
  Purchase #7 $48.36   10.517%   $53.446   $53.45   $53.45   $53.40  
  7 purchase totals = $1,025.85       $1,124.8473   $1,124.86   $1,124.90   $1,124.80