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 $219.51   3.214%   $226.5651   $226.57   $226.55   $226.60  
  Purchase #2 $223.99   12.418%   $251.8051   $251.81   $251.80   $251.80  
  Purchase #3 $114.29   9.601%   $125.263   $125.26   $125.25   $125.30  
  Purchase #4 $248.44   6.831%   $265.4109   $265.41   $265.40   $265.40  
  Purchase #5 $161.67   12.337%   $181.6152   $181.62   $181.60   $181.60  
  Purchase #6 $21.55   11.186%   $23.9606   $23.96   $23.95   $24.00  
  Purchase #7 $114.52   11.148%   $127.2867   $127.29   $127.30   $127.30  
  7 purchase totals = $1,103.97       $1,201.9066   $1,201.92   $1,201.85   $1,202.00