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 $9.86   8.385%   $10.6868   $10.69   $10.70   $10.70  
  Purchase #2 $238.94   7.123%   $255.9597   $255.96   $255.95   $256.00  
  Purchase #3 $160.44   7.444%   $172.3832   $172.38   $172.40   $172.40  
  Purchase #4 $210.70   4.419%   $220.0108   $220.01   $220.00   $220.00  
  Purchase #5 $57.68   12.537%   $64.9113   $64.91   $64.90   $64.90  
  Purchase #6 $236.37   10.866%   $262.054   $262.05   $262.05   $262.10  
  Purchase #7 $234.35   7.241%   $251.3193   $251.32   $251.30   $251.30  
  7 purchase totals = $1,148.34       $1,237.3251   $1,237.32   $1,237.30   $1,237.40