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 $105.69   12.755%   $119.1708   $119.17   $119.15   $119.20  
  Purchase #2 $207.41   3.293%   $214.24   $214.24   $214.25   $214.20  
  Purchase #3 $185.84   12.841%   $209.7037   $209.70   $209.70   $209.70  
  Purchase #4 $156.28   11.601%   $174.41   $174.41   $174.40   $174.40  
  Purchase #5 $112.57   9.634%   $123.415   $123.42   $123.40   $123.40  
  Purchase #6 $238.50   6.327%   $253.5899   $253.59   $253.60   $253.60  
  Purchase #7 $201.89   11.157%   $224.4149   $224.41   $224.40   $224.40  
  7 purchase totals = $1,208.18       $1,318.9443   $1,318.94   $1,318.90   $1,318.90