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 $23.94   3.788%   $24.8468   $24.85   $24.85   $24.80  
  Purchase #2 $231.80   10.234%   $255.5224   $255.52   $255.50   $255.50  
  Purchase #3 $243.91   8.676%   $265.0716   $265.07   $265.05   $265.10  
  Purchase #4 $28.81   12.847%   $32.5112   $32.51   $32.50   $32.50  
  Purchase #5 $91.82   6.371%   $97.6699   $97.67   $97.65   $97.70  
  Purchase #6 $163.36   8.233%   $176.8094   $176.81   $176.80   $176.80  
  Purchase #7 $191.92   9.716%   $210.5669   $210.57   $210.55   $210.60  
  7 purchase totals = $975.56       $1,062.9982   $1,063.00   $1,062.90   $1,063.00