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 $120.70   11.524%   $134.6095   $134.61   $134.60   $134.60  
  Purchase #2 $236.52   7.109%   $253.3342   $253.33   $253.35   $253.30  
  Purchase #3 $14.63   13.530%   $16.6094   $16.61   $16.60   $16.60  
  Purchase #4 $229.71   10.816%   $254.5554   $254.56   $254.55   $254.60  
  Purchase #5 $95.28   7.801%   $102.7128   $102.71   $102.70   $102.70  
  Purchase #6 $117.67   4.163%   $122.5686   $122.57   $122.55   $122.60  
  Purchase #7 $131.42   5.825%   $139.0752   $139.08   $139.10   $139.10  
  7 purchase totals = $945.93       $1,023.4651   $1,023.47   $1,023.45   $1,023.50