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 $12.33   10.153%   $13.5819   $13.58   $13.60   $13.60  
  Purchase #2 $184.30   12.727%   $207.7559   $207.76   $207.75   $207.80  
  Purchase #3 $213.42   13.240%   $241.6768   $241.68   $241.70   $241.70  
  Purchase #4 $219.87   9.809%   $241.437   $241.44   $241.45   $241.40  
  Purchase #5 $114.30   6.755%   $122.021   $122.02   $122.00   $122.00  
  Purchase #6 $105.96   5.549%   $111.8397   $111.84   $111.85   $111.80  
  Purchase #7 $203.69   11.615%   $227.3486   $227.35   $227.35   $227.30  
  7 purchase totals = $1,053.87       $1,165.6609   $1,165.67   $1,165.70   $1,165.60