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 $112.51   13.206%   $127.3681   $127.37   $127.35   $127.40  
  Purchase #2 $216.28   13.598%   $245.6898   $245.69   $245.70   $245.70  
  Purchase #3 $54.29   13.596%   $61.6713   $61.67   $61.65   $61.70  
  Purchase #4 $71.75   13.809%   $81.658   $81.66   $81.65   $81.70  
  Purchase #5 $235.83   4.498%   $246.4376   $246.44   $246.45   $246.40  
  Purchase #6 $221.40   10.287%   $244.1754   $244.18   $244.20   $244.20  
  Purchase #7 $40.43   3.399%   $41.8042   $41.80   $41.80   $41.80  
  7 purchase totals = $952.49       $1,048.8044   $1,048.81   $1,048.80   $1,048.90