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 $180.48   11.567%   $201.3561   $201.36   $201.35   $201.40  
  Purchase #2 $138.44   6.479%   $147.4095   $147.41   $147.40   $147.40  
  Purchase #3 $125.79   6.698%   $134.2154   $134.22   $134.20   $134.20  
  Purchase #4 $85.94   11.209%   $95.573   $95.57   $95.55   $95.60  
  Purchase #5 $90.79   11.301%   $101.0502   $101.05   $101.05   $101.10  
  Purchase #6 $115.29   5.427%   $121.5468   $121.55   $121.55   $121.50  
  Purchase #7 $226.81   11.808%   $253.5917   $253.59   $253.60   $253.60  
  7 purchase totals = $963.54       $1,054.7427   $1,054.75   $1,054.70   $1,054.80