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 $250.69   7.571%   $269.6697   $269.67   $269.65   $269.70  
  Purchase #2 $207.89   6.616%   $221.644   $221.64   $221.65   $221.60  
  Purchase #3 $219.52   7.473%   $235.9247   $235.92   $235.90   $235.90  
  Purchase #4 $101.62   13.444%   $115.2818   $115.28   $115.30   $115.30  
  Purchase #5 $132.70   5.238%   $139.6508   $139.65   $139.65   $139.70  
  Purchase #6 $67.82   6.182%   $72.0126   $72.01   $72.00   $72.00  
  Purchase #7 $181.41   4.631%   $189.8111   $189.81   $189.80   $189.80  
  7 purchase totals = $1,161.65       $1,243.9947   $1,243.98   $1,243.95   $1,244.00