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 $53.67   5.539%   $56.6428   $56.64   $56.65   $56.60  
  Purchase #2 $219.97   7.647%   $236.7911   $236.79   $236.80   $236.80  
  Purchase #3 $16.82   11.348%   $18.7287   $18.73   $18.75   $18.70  
  Purchase #4 $197.70   5.860%   $209.2852   $209.29   $209.30   $209.30  
  Purchase #5 $21.37   11.773%   $23.8859   $23.89   $23.90   $23.90  
  Purchase #6 $200.88   4.560%   $210.0401   $210.04   $210.05   $210.00  
  Purchase #7 $235.46   9.857%   $258.6693   $258.67   $258.65   $258.70  
  7 purchase totals = $945.87       $1,014.0431   $1,014.05   $1,014.10   $1,014.00