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 $168.69   6.499%   $179.6532   $179.65   $179.65   $179.70  
  Purchase #2 $64.69   7.646%   $69.6362   $69.64   $69.65   $69.60  
  Purchase #3 $44.43   3.365%   $45.9251   $45.93   $45.95   $45.90  
  Purchase #4 $248.47   8.830%   $270.4099   $270.41   $270.40   $270.40  
  Purchase #5 $26.55   8.143%   $28.712   $28.71   $28.70   $28.70  
  Purchase #6 $211.85   8.367%   $229.5755   $229.58   $229.60   $229.60  
  Purchase #7 $179.85   8.438%   $195.0257   $195.03   $195.05   $195.00  
  7 purchase totals = $944.53       $1,018.9376   $1,018.95   $1,019.00   $1,018.90