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 $114.41   6.582%   $121.9405   $121.94   $121.95   $121.90  
  Purchase #2 $106.67   13.109%   $120.6534   $120.65   $120.65   $120.70  
  Purchase #3 $20.41   10.539%   $22.561   $22.56   $22.55   $22.60  
  Purchase #4 $219.25   5.870%   $232.12   $232.12   $232.10   $232.10  
  Purchase #5 $207.51   13.274%   $235.0549   $235.05   $235.05   $235.10  
  Purchase #6 $159.77   8.754%   $173.7563   $173.76   $173.75   $173.80  
  Purchase #7 $187.32   6.354%   $199.2223   $199.22   $199.20   $199.20  
  7 purchase totals = $1,015.34       $1,105.3084   $1,105.30   $1,105.25   $1,105.40