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 $57.93   7.409%   $62.222   $62.22   $62.20   $62.20  
  Purchase #2 $6.49   4.545%   $6.785   $6.79   $6.80   $6.80  
  Purchase #3 $30.39   3.239%   $31.3743   $31.37   $31.35   $31.40  
  Purchase #4 $243.50   10.807%   $269.815   $269.82   $269.80   $269.80  
  Purchase #5 $183.71   9.153%   $200.525   $200.53   $200.55   $200.50  
  Purchase #6 $249.37   5.232%   $262.417   $262.42   $262.40   $262.40  
  Purchase #7 $210.57   12.536%   $236.9671   $236.97   $236.95   $237.00  
  7 purchase totals = $981.96       $1,070.1054   $1,070.12   $1,070.05   $1,070.10