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 $61.65   7.407%   $66.2164   $66.22   $66.20   $66.20  
  Purchase #2 $184.32   10.643%   $203.9372   $203.94   $203.95   $203.90  
  Purchase #3 $241.95   4.274%   $252.2909   $252.29   $252.30   $252.30  
  Purchase #4 $13.87   12.364%   $15.5849   $15.58   $15.60   $15.60  
  Purchase #5 $155.48   10.670%   $172.0697   $172.07   $172.05   $172.10  
  Purchase #6 $198.48   3.418%   $205.264   $205.26   $205.25   $205.30  
  Purchase #7 $234.53   7.441%   $251.9814   $251.98   $252.00   $252.00  
  7 purchase totals = $1,090.28       $1,167.3445   $1,167.34   $1,167.35   $1,167.40