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 $243.45   9.461%   $266.4828   $266.48   $266.50   $266.50  
  Purchase #2 $211.87   9.193%   $231.3472   $231.35   $231.35   $231.30  
  Purchase #3 $197.59   11.783%   $220.872   $220.87   $220.85   $220.90  
  Purchase #4 $166.71   5.765%   $176.3208   $176.32   $176.30   $176.30  
  Purchase #5 $218.74   3.179%   $225.6937   $225.69   $225.70   $225.70  
  Purchase #6 $60.65   10.592%   $67.074   $67.07   $67.05   $67.10  
  Purchase #7 $231.27   7.205%   $247.933   $247.93   $247.95   $247.90  
  7 purchase totals = $1,330.28       $1,435.7235   $1,435.71   $1,435.70   $1,435.70