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 $240.63   10.647%   $266.2499   $266.25   $266.25   $266.20  
  Purchase #2 $207.80   11.306%   $231.2939   $231.29   $231.30   $231.30  
  Purchase #3 $244.39   7.261%   $262.1352   $262.14   $262.15   $262.10  
  Purchase #4 $114.26   7.241%   $122.5336   $122.53   $122.55   $122.50  
  Purchase #5 $143.96   4.423%   $150.3274   $150.33   $150.35   $150.30  
  Purchase #6 $72.50   6.465%   $77.1871   $77.19   $77.20   $77.20  
  Purchase #7 $52.31   7.172%   $56.0617   $56.06   $56.05   $56.10  
  7 purchase totals = $1,075.85       $1,165.7888   $1,165.79   $1,165.85   $1,165.70