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 $222.62   13.801%   $253.3438   $253.34   $253.35   $253.30  
  Purchase #2 $54.55   11.476%   $60.8102   $60.81   $60.80   $60.80  
  Purchase #3 $64.37   8.243%   $69.676   $69.68   $69.70   $69.70  
  Purchase #4 $139.71   3.555%   $144.6767   $144.68   $144.70   $144.70  
  Purchase #5 $250.62   5.515%   $264.4417   $264.44   $264.45   $264.40  
  Purchase #6 $86.52   13.723%   $98.3931   $98.39   $98.40   $98.40  
  Purchase #7 $232.97   12.494%   $262.0773   $262.08   $262.10   $262.10  
  7 purchase totals = $1,051.36       $1,153.4188   $1,153.42   $1,153.50   $1,153.40